For TV comedy, Fey and Poehler. Fay was good in Date Night also. Oh and Jane Lynch.
Movie comedy – I can’t think of a standout. Oh, wait, Amy Adams for sure. Kudrow was great in The Opposite of Sex but I can’t think of any other great comedic movie roles for her.
Betty White.
The best comedic actress in movies is Candace Bergen, but of course, she doesn’t get leading roles anymore.
The problem is that actresses who are genuinely good at comedy – women like Bullock and Reese Witherspoon – want to be taken seriously. Which, in Hollywood, means getting the hell out of comedy and playing “serious” parts.
Mindy Kaling is great on The Office, and she’s bene funny in the few small movie roles I’ve seen her in but she seems to be avoiding the “movie star” path.
For someone who’s actually been a main part of movies, I think it might be Anna Faris currently. As The Onion said “She’s been the best part of a lot of bad movies”. She’s even watchable in the Scary Movie series.
Jennifer Coolidge.