I was thinking about this subject the other day when I heard that Ellen Degeneres is going to host the Oscars this year. (Someone told me once that I look like Ellen...what the...? but that's another story). So here are some women who I think are funny:
Actors/movie stars:
Parker Posey
Catherine O'Hara
-> both Christopher Guest regulars
Toni Collette
Elaine Benes (yes, the character, not the actress in her other roles I've seen)
I think Ellen is sorta funny
OK, so that list is rather short. I'm not including women in romantic comedies who have funny roles (i.e Meg Ryan or Julia Roberts); I'm talking about truly comedic women here.
So here are women I know personally who have a witty way about them:
Grandma Belz and her sisters (especially the late Aunt Billie)
My mom and her two sisters, Sara and Julie
Sisters-in-law Kim and Andrea
There are several other women who are not related to me who I know will make me laugh whenever I'm around them, but for the sake of brevity I won't name them all here. My point is this: it seems that funny men are a dime a dozen, but when I come across a truly comedic woman, she is usually much more funny to me than a room full of funny men. Case in point: my grandmother could outwit a roomful of my uncles any day of the week.

What about Emma Thompson in "Wit"? OK, maybe that doesn't count.
Lisa Ayres Loney and Sara Donaldson both come to mind.
I think Hope Davis is very witty, although often she descends into the slapstick. Don't take that personally, Hope. I'm just saying you have the whole package.
OK, now we are naming people we know. I was thinking specifically of Marylu Carl and Barb Schreur. I had forgotten about Hope (sorry Hope). And I think it's "Sarah" Donaldson, isn't it, not "Sara?"
Once I got mentioned in Josiah's blog as a cloud in the "Mario" video from Gordon making the web rounds. But that ain't nothin' compared to being in the same blog entry as Grandma Belz and Sarah Donaldson! Now I have truly arrived.
I like this entry and topic. Hitch wrote an article not long ago arguing that there is no such thing as a truly funny woman. Have a read in the January Vanity Fair... I think somebody linked to a blog copy if you try googling it as it is not online or for free.
I disagree with him of course (forced alibi :)) and will defend the humour of such above mentioned females in all senses of the word.
Yeah, if I were drunk, standing on my head, and singing Tiny Bubbles in the rain, I think I might confuse you with Ellen, but only for a moment.