Milla Jovovich, John Candy, Helena Bonham Carter, Michael Caine. I hope that is random enough to keep you going for a while, haha.
The Fifth Element - By far my favourite with her and one of my favourite movies, period.
Resident Evil - I don't think I need to explain.
Ultraviolet - Only because of how stunning she was in it, the movie itself was quite shit except for the last fight scene.
John Candy: I haven't seen enough to have a top three. I've only ever really seen Spaceballs and that's not really my kind of movie.
Helena Bonham Carter (she's on my list of actors filmographies to work through, just haven't gotten around to it yet):
Fight Club - Marla Singer is one of my all time favourite characters and no one could've done her better than she did.
The King's Speech - I really enjoyed seeing her in a very quiet but still quirky role.
I would probably have put Bellatrix Lestrange up there if it was only about characters.
Michael Caine (haven't gotten around to watching any of his older movies yet):