Actually, I did see Charlize Theron in The Astronaut’s Wife, so pffft!
She’s my favorite African American actress. 
Harry Dean Stanton has never failed to make anything he was in better.
Beth Grant.
Who’s she?
Jeff Bridges and Beau Bridges. Michelle Pfeiffer while we are on the cast of The Fabulous Baker Boys. She did her own damn good singing.
A dark-haired woman with a twang in her accent who usually plays small but interesting roles. Examples: the pageant organizer in Little Miss Sunshine, the dance team coach in Donnie Darko, the mother of Moss’s wife in No Country for Old Men, etc.
I would have to add Bill Murry.
What’s funny is that I saw her in this week’s Entertainment Weekly an hour after I turned off the computer – they have a piece on “really good actors who always work but aren’t household names,” and she’s one of them.
Brian Blessed. I put it that size because that’s how he would say it.
Ian McKellan
I second Parker Posey. Hell, she made Blade: Trinity watchable.
That’s who I came in here to mention. I referred to her in real life as one of my favorite actresses, and people usually say “Who?” My response is “I can practically guarantee you’ve seen at least one of her movies, and probably more than one, but didn’t even realize it was the same person. She’s that good.”
I’ve sometimes felt sorry for Ms. Collette because she’s apparently not Hollywood beautiful enough to get leading lady roles, but she’s getting plenty of roles and is able to play a broader range of characters than just romantic leads. Even when her characters may be superficially similar, like in Sixth Sense and About a Boy (worried single mother of a troubled, oddball son) she makes them totally different people.
I think that Christopher Guest may get more credit as a writer/director than as an actor, but compare just his two most famous roles (Nigel in This Is Spinal Tap and Count Rugen in The Princess Bride) and it should be clear that he’s a very talented performer.
Toni Collette is also excellent as Greg Kinnear’s wife in Little Miss Sunshine.
She completely nails the American accent, too.
After watching some of the suggestions in this thread, I can confidently add William Fichtner to this list.
Also, Jason Isaacs. He’s played at least three cartoonish, mustache-twirling villians, and he gave each of them distinct, nuanced personalities. In my eyes he can do no wrong.
bump to say You know who else is always good?
Kevin Kline.
(I’ve got DeLovely on in the background as I do some work.)
Here’s another. Best actor in the world.
Best actress? Kate Winslet. When has she ever put in a bad performance? Even in shitty movies, like “The Life of David Gale,” she’s first rate.
I saw Kevin Kline playing Falstaff in a production of Henry IV Part 2. He was brilliant. That was probably the most enjoyable evening I’ve ever spent in the theater. The end of the play, in which Henry rejects Falstaff, was quite powerful. After yukking it up for a couple of hours, Kline really pulled off the emotional transition well, leaving me just sort of dumbstruck (to my shame, I had not read the play and didn’t know the plot beforehand, but it meant I got to be surprised).
Good news for Toni Collette fans: she’s the lead in the new Showtime series The United States of Tara, where she plays a woman with multiple personalities. The show was developed by Diablo Cody, who won an Oscar last year for writing Juno. According to the wikipedia page, it premieres on January 18, 2009. It looks interesting and I’ll definitely give it a look.
Helen Mirren. Even in painfully creaky made-for-tv crap like the Ayn Rand bio-pic, she is regal.
IS always good:
M. Emmet Walsh
Philip Baker Hall
WAS always good:
Warren Oates