Twin Peaks People!
OK. This is an attempt to give little character descriptions. If I left anyone out, please let me know. But I'm really only doing this for the main characters. So if I left out your cousin, who was an extra, and you can see her foot at one point, don't let me know.
At the Sheriff's Station/FBI:
Harry S. Truman: What a man. Remember when he and Josie are fooling around and she's wearing her new silk robe and she says "rip it," and he just tears that thing in half? I love that. What a sexpot. Anyway, obviously Truman is the Sheriff of Twin Peaks. He is 2nd in command to Cooper once he arrives. He is having an affair with Josie Packard. Does not seem to have any family or anything going on in his life other than his job. Poor guy. Poor, sexy, guy.
Andy Brennan: The dim-witted deputy who takes to crying at sentimental moments and had never used his gun before Cooper taught him how. The often-targeted victim of Rosenfield's nasty comments, Andy is dating Lucy Moran.
<Hawk: He's kinda sexy too. . . anyway, Hawk is the other deputy in Twin Peaks, definitely more intelligent than Andy. Given to relying on the folklore and beliefs of his heritage, Native American, in his policing duties. No visible girlfriend, but we are told he is dating "Diane Shapiro, Ph.D., Brandeis."
Lucy Moran: The Sheriff's station secretary. Also dim-witted and prone to taking much too long to get to the point of anything. Dating Deputy Andy and Dick Tremaine of men's fashions at Horne's Department Store.
Dale Cooper: Ah. . . my Special Agent. The super-sexy, super-intelligent and often super-weird FBI agent who is assigned to the case of Laura Palmer's murder. His arrival in Twin Peaks marks the change of standard police work in town, as Cooper relies on his weird dreams, his visions, other people's visions, Tibetan folklore, and anything else to solve crimes. Has Audrey Horne wetting herself anytime she sees him; but is still upset over the death of his first love, Caroline. Begins to date, and falls in love with, Annie Blackburn.
Gordon Cole: David Lynch's character, the FBI agent and Cooper's boss, is a rare appearance, but always a good one. He's next to deaf and therefore shouts at everyone and requires that everyone shout at him. Has very good, slick FBI-man intuition, lets Cooper have fun with his dreams and visions and such. Falls head over heels for Shelley Johnson.
Albert Rosenfield: Definitely one of the best characters on the series, but Albert's appearances, too, are rare. Every word out of this FBI special agent's mouth is sarcastic, biting, and mean (but hysterical). No known girlfriend or wife, but loves Sheriff Truman.
Diane: Ah, Diane. The elusive enigma of Cooper's Diane. Some have thought that its just Cooper's pet name for his recorder thingy, but other facts lead me to believe that she his his secretary back at the Bureau. We never see her, or even hear her voice.The Palmer Family:
Laura: The girl who was found murdered and whose death created Twin Peaks. She was the homecoming queen and popular....although we don't see her in the series (um, she's dead) we meet her in FWWM. She was dating Bobby Briggs and James Hurley, and, we find out, was a cocaine addict and prostitute. Which means that she's slept with most of Twin Peaks, including Jacques Renault, Leo Johnson, Ben Horne. Tomented for most of her life by BOB, she most likely allowed herself (or at least was ready) to be killed to escape him. Best friend was Donna Hayward.
Leland: The Palmer family patriarch, the attorney for the Hornes. Likes to sing, dance, visit prostitutes. Provided the first body for BOB.
Sarah: Laura's mother, she is mostly a very sympathetic, depressed, deprssing character throughout the series, as she never quite gets over the death of her only child. 
Madeline Ferguson:"They're cousins, identical cousins. . ." sorry. Maddy is the cousin of Laura Palmer, and looks strikingly similar to her. Visits her aunt and uncle after Laura's death, quickly becomes involved in the case by helping Donna and James do their thing. Was very close to Laura, wants to get very close to James, pisses Donna off.The Hayward Family:
Donna: Laura Palmer's best friend, was dating Mike Nelson before she dates James Hurley. Wants to help solve Laura's case, gets in everybody's way.
Doc: Donna's "father", everyone in Twin Peaks' physician. Identified Laura's body. Good friend to the folks at the sheriff's station.
Eileen: The mother. . .we don't see her too much either. In a wheelchair for unknown reasons. Turns out she's had an affair with Ben Horne. . . with obvious consequences.The Horne Family:
Audrey: In Laura and Donna's class at school, was more of an aquaintance than friend to Laura. Also gets drawn into the case by her discoveries about Horne's Department Store, One Eyed Jack's. Thus, she has a breif stint with prostitution and heroin. Is desperately in love with Agent Cooper (who isn't?), later falls in love with John Justice Wheeler.
Ben: Audrey's father, owner of Horne's Department Store, One Eyed Jack's, most of Twin Peaks. Spends much of the series trying to get his development plan, Ghostwoods, to a buyer. Having an affair with Catherine Martell. Goes slightly crazy for a while and wins the Civil War for the South.
Jerry: Ben's brother. . .a little weird. Spends much of his time a One Eyed Jack's and eating. Eating odd things. He and Ben are both really into food. Not dating anybody, not since Snow Queen Heba.
Sylvia: Audrey's mom. . .hardly ever in the series. . .seems like one of those rich, depressed women who probably know their husbands are cheating and just don't care anymore.
Johnny: Audrey's mentally retarded older brother. He was tutored by Laura Palmer and seems to miss her absence.The Johnson Family:
Leo: Ew. probably the least liked character in the whole series. Married Shelley before she was out of high school, forcing her to drop out and basically become his domestic slave. Occupation as a truck driver, spends long hours on the road when he's not beating his wife or visiting prostitutes. Key role in Laura's murder. Part of a big drug ring run in Twin Peaks. After he becomes a vegetable, becomes right hand man for Windham Earle.
Shelley: Married to Leo, having an affair with Bobby Briggs. Spens most of her time at work, as a waitress at the RR Diner. Never really gets into the whole Laura case, as she is pretty much ignorant of Leo's whole involvement with everything. Later serves as Gordon Cole's one true love.The Briggs Family:
Bobby: Dating Laura Palmer, Shelley Johnson. Supplies cocaine to the high school kids who crave it. In the series, James reports that Laura cryptically told him that Bobby had "killed a guy"; in FWWM, we learn that he shot and killed drug dealer Mike. Hates James Hurley. Friends with Mike Nelson.
Major:The Major's role in everything is "classified". Really, he is a military man working on Project Blue Book, which, although classified, in real life had something to do with UFOs and in Twin Peaks the Major reveal that PBB is concerned with finding the White Lodge. A very serene, patient, loving man, who helps out the police whenever he can.Betty: Bobby's mother, we never really see her. Loves her family very much.
The Hurley Family:
James: The bad biker dude, the token James Dean character. Loved Laura Palmer, loves Donna Hayward, attracted to Maddy's Laura-ness. He's a good boy.
Ed: James' uncle, owns Big Ed's Gas Farm, married to Nadine, having an affair with Norma Jennings. Is a Bookhouse Boy, and as such is good friends with the good people over at the Sheriff's station.
Nadine: Ed's wife. Ed shot her eye out on their honeymoon hunting trip, she now wears an eye patch. Bitter woman until she tries to committ suicide. Then she has superhuman strength and begins to think she's 16 again and goes to high school, where she falls in love with Mike Nelson (and she dates him).The Jennings/Niles/Blackburn Family:
Norma Jennings: Owner of the RR Diner. Husband Hank is in jail; she's having an affair with Ed Hurley.
Hank Jennings: In jail until he makes parole (duh), when he begins to work for Norma's diner and love. Does not like Ed (he's aware of his wife's affair). Mysterious ties to Jacques Renault, Josie Packard, and Ben Horne.
Vivian Jennings/Niles: Norma's mom, also the mysterious Wendt food crtitic. Norma decides that the emotional abuse from her mother is too much, especailly after she kills the RR in a food review, so Vivian is on the show for about 3 episodes.
Ernie Niles: Vivan's new husband, who has mysterious ies to hank Jennings. he's some sort of reformed convict, although he gets back onto criminal activity with hank and the boys at One Eyed Jacks.
Annie Blackburn:Norma's sister, who has been a nun and lived in a convent all her life. Comes to Twin Peaks and works at the Diner, where she is constantly in awe of reality (outside a convent) and snags Agent Cooper. Also seen as a bloody mess in Laura Palmer's bed in FWWM.The Martell/Packard Family:
Catherine Martell:The sister of Andrew, and the wife of Pete, who together run the saw mill. Having an affair with Ben Horne. Powerful business woman. Hates Josie. Moonlights as a Japanese business man form time to time.
Pete Martell:The sweet man who found Laura's body. Married to Catherine, favors Josie, spends most of him time fishing.
Andrew Packard:Catherine's brother, who "died" in a mysterious boating accident. He married Josie in Hong Kong and left her the saw mill in his will, much to the dismany of catherine, who got nothing.
Josie Packard:The beautiful widow of Andrew Packard, she's now dating Sheriff Truman. She owns the saw mill and is also a powerful business woman. She and Ben Horne have a busisness relationship, planning to do over Catherine.The Spirit Family:
See my theory section for a fuller explanation of all these spirits.
BOB:The most evil in all of Twin Peaks. Inhabits a few bodies over the course of the series, most notably that of Leland Palmer. He is responsible for the deaths of Laura Palmer, Theresa Banks and a few others.
Mike:Once the evil partner of BOB< he cut of his arm and became good. His mission is now to stop BOB. Inhabits the body of Philip Gerard. 
LMFAP:The dwarf who lives in the Red Room, we see him in Cooper's dreams. He is most likely Mike's arm, and therfore is a bad spirit.
Giant: A good spirit who inhabits the White Lodge, he comes to Cooper in visions and dreams and gives him clues for the case.
Mrs. Tremond and grandson:Also good spirits, they come to the mortal realm, it seems, to help people with the case as well. They also appeared to Laura in FWWM.Others:
The Log Lady: The Log Lady serves for a little amusement in Twin Peaks, as most regard her as crazy. She does somehow communicate with her Log, and the log ends up giving important clues to Laura's death and especially regarding the Black Lodge.
Mike Nelson:Donna's ex-boyfriend, Bobby's best friend, then Nadine's love interest and boyfriend. Doesn't really play a vital role in anything.
Blackie:The, um, proprieter? of One Eyed Jacks. Ties to Jacques Renault and drugs, was Laura's boss when she worked there.
The Renaults:The three brothers. Jacques is the bartender at One Eyed Jacks and a major player in the drug ring. Has had sex with Laura Palmer and was one of the men present the night she was killed. Of course, is later killed by Leland Palmer. Brother Bernard is into Blackie and drugs. Brother Jean was killed early on by Leo, but also into drugs and Blackie's sister Nancy.
Ronnette Pulaski:A prostitute with Laura, she was present when Laura was killed, and was almost killed herself. Helps identify BOB once she comes out of her state of shock.
Theresa Banks:The young prostitute who was killed (by BOB/Leland) a year before Laura was. Gordon Cole and Cooper think that the cases are related; that why Cooper was sent to investigate Laura's case. We only hear about her in the series; we meet her briefly in FWWM.
Dr. Jacoby:The town psychiatrist. Has a thing for Hawaii and is a hippie. Was doing therapy with Laura Palmer; was in love with her (too).
Harold Smith:Laura's agoraphobic friend from the Meals On Wheels program. She told him about BOB and gave him her secret diary. He was in love with her too. Later, Donna befriends him and he falls for her too. 
Windham Earle: Cooper's old FBI partner. He went crazy after Cooper fell in love with his wife and she later died. He worked on Project Blue Book alongside Major Briggs, but was kicked off when he began to look for the evil of the Black Lodge rather than the good of the White.