Tina Fey fought not to do Sarah Palin:

From MSNBC:

LOS ANGELES - Tina Fey just scored a Best Actress Emmy for playing frazzled head writer Liz Lemon on “30 Rock,” but it was the thought of playing Sarah Palin on “Saturday Night Live” a week ago that left the comedian herself frazzled.
On the Emmy red carpet, Fey revealed to Access Hollywood’s Billy Bush she actually refused to play her political look-a-like when it was first proposed.
“I was fighting them all week on it,” Fey said. “I kept saying, ‘I don’t want to do it, I’m not an impressionist.’ I kept telling (‘SNL’ producer) Lorne (Michaels), ‘No! I’ll show up ... I’ll do anything except play her. I can’t do it.’ Then, I was worn down. Lorne wore me down by the end of the week.”

Fey, whose “30 Rock” also picked up the Emmy for Best Comedy Series, Best Writing for a Comedy Series, and Best Actor (for co-star Alec Baldwin), said she was fortunate the figurehead she had to impersonate had an unusual accent.
“Sarah Palin has a crazy voice. I would say, not since ‘Sling Blade’ has there been a person who’s really easy to imitate, so I got really lucky on that one,” Fey said.
While Gov. Palin herself reportedly enjoyed the impersonation, John McCain advisor Carly Fiorina called Fey’s portrayal “sexist.” So what did Tina think about that response? Apparently, not much.
“I saw one lady trying to form a thought that it was sexist on the news but she didn’t get it together, probably because she was a lady and she was dumb,” Fey said. “Wait is that sexist?”
In related news, as previously reported on AccessHollywood.com, Oprah Winfrey recently filmed a cameo for “30 Rock,” and Fey told Billy Bush having the TV talk show queen on set was simply “delightful.”
“Whenever anyone would say, ‘Who is your dream person?’ I would always say, ‘Oprah! Oprah!’” Fey said. “Somehow we convinced her to do it. I think (Oprah’s best friend) Gayle helped talk her into it and then she came and shot with us and she was delightful!”

And Jennifer Aniston, who also appears on this season’s “30 Rock,” made the set another thrilling experience for the cast and crew.
“They were very happy to have a real TV star on our show,” Fey laughed. “She was great, too ... She plays an old Chicago roommate of mine and Jane Krakowski’s character. We have a name for her that you can’t really say on TV.”