5. "The Godfather" and "The Godfather Part II" (1972, 1974)
Poor Kay Adams. She wasn't Michael Corleone's first love (that honor went to the beautiful girl/wife in Sicily who was blown up in a car) but she was the appropriate choice. A WASPy, maternal type who added to Michael's respectability, Keaton's Kay remained relatively silent throughout the first picture, living in willful ignorance of Michael's, uh, lifestyle and business dealings. But when he closed the door on her (in the original film's famous final scene) the problems really started. One of her greatest moments in the entire saga is during a domestic battle with Michael, during which she reveals she didn't lose her baby, but horrors, aborted it. The moment is absolutely shattering, and you feel sorry for Kay (you really feel bad for her), but also for Michael, who started the disintegration of the family in the first place -- this is the result. One of Keaton's finest moments.

4. "Manhattan" (1979)
It takes talent to make a character who is, at first, pretty pretentious and annoying into an actually likeable character whom you come to care about. Such is Diane Keaton's Mary in Woody Allen's classic "Manhattan." She's the woman who's having an affair with Allen's best friend (played by Michael Murphy) but is dumped when the relationship endangers his marriage. She moves on to Allen who, in classic romantic comedy style, can't stand each other on first meeting. She hates the art he likes, the composers he admires and thinks Bergman is overrated. Allen is fascinated nonetheless and the two begin a friendship (while Allen dates a 17-year-old played by Mariel Hemingway) that morphs into romance. It's an unlikely union between two self obsessed, neurotic smarty pants but it's witty and romantic and sad all at once. Keaton is terrific -- insecure (Allen claims her self esteem must be a "notch below Kafka's") while being completely full of herself. In other words, real. Incompatibility has never been so romantic.

3. "Reds" (1981)
Though some critics thought Keaton not sexy enough to play the, lets face it,
sexy radical Louise Bryant in Warren Beatty's fantastic epic "Reds," Keaton nails the part -- partly for her own skills as an actress and partly for the company around her. When a sublime Jack Nicholson (playing Eugene O'Neill) calls you a "heartbreaker," you are one. And when Warren Beatty's famed journalist/communist activist finally asks you to marry him (even when he really doesn't believe in it), you're holding some serious sway over these men. Playing the real-life Bryant as frequently insecure and intimidated but uninhibited and a true "Queen of Bohemia" (as her biographer proclaimed her), Keaton conveys a potent mixture of vulnerability, sexuality and manipulation. Her scenes with Nicholson absolutely sizzle and her arguments with Beatty (a lover offscreen as well) are so convincing, you'd think their fights were real. Were they?

2. "Looking for Mr. Goodbar" (1977)
What's a nice girl like Diane Keaton doing in a movie like this? That's what many a viewer thought while watching Richard Brooks' disturbing, sexual and violent "Looking for Mr. Goodbar," a notorious movie that continues to confuse with its moral message. Is the film judging the sexually free, hedonistic life of Keaton's character, or is it judging the world surrounding her -- a world full of darkness and bad luck and consequences? What kind of cautionary tale is it? The film remains remarkably subversive (and unanswerable) and incredibly strong, chiefly with the very nice presence of Keaton. Adapted from Judith Rossner's bestselling book, Keaton plays lonely and lost Theresa -- a sweet young woman who teaches first grade to deaf-mutes by day and makes herself available at the singles bars by night. And she really makes herself available. Through many sexual encounters, some more disturbing than others, we watch Keaton's Theresa, perhaps masochistically, delve into a promiscuity rarely seen by leading ladies. And she's not just playing the "tramp" -- she truly is confused. Keaton is perfect in the role because she looks like the girl you take home to mom. Her line delivery is wonderfully distracted, and every giggle or aside subtly reveals her avoidance to the deeper truth about herself. It's a bravura, shocking and ultimately heartbreaking performance and Keaton's bravest work to date.

1. "Annie Hall" (1977)
You've seen a lot of Woody Allen on this list, which is simply unavoidable, as so much of Keaton's appeal is best displayed in Allen's pictures. And no more is this evident in Keaton's most famous, most iconic role -- as the quirky, eponymous leading lady of Allen's masterpiece, "Annie Hall." Where to begin? There's the romance between neurotic comedy writer Alvie Singer (Allen) and the kooky aspiring singer Annie (Keaton), a woman who drives insanely, sits nice with her secretly crazy WASP family (well, her brother, played by Christopher Walken, is nuts), dons lots of spiffy Ralph Lauren menswear and says things like "la-di-da." Keaton is such a wonderfully "New York" character -- not overtly feminine, and yet very much a woman; a little daffy and up for new experiences (like reading The National Review), and yet continually wholesome. In other hands, Annie could have been too dizzy (annoying even), but when she calls Alvie in the middle of the night to kill a spider "the size of a Buick," it actually melts your heart when you learn she really just misses him. And who can forget their lobster date? So, so charming. Not only will there never be another Annie Hall, there'll never be an actress like Diane Keaton to play her.

What is your favorite Diane Keaton performance? Write us at heymsn@microsoft.com

Kim Morgan is a film writer for the LA Weekly, Fandango and Reel.com. She was a film critic for The Oregonian and has written about movies for various print and Web media. She served as DVD critic on Tech TV's "The Screen Savers" and has appeared as guest film critic on AMC's "The Movie Club with John Ridley" and on E! Entertainment. She writes for her blog Sunsetgun.com.