Jennifer Tilly is an actress who's better known for her voiceover work than she is for her live-action roles, but her roles have been so diverse and interesting that you can't really fault her for that.
Tilly has voiced Bonnie on Family Guy from 1999 to 2013, but she's probably best known for Monsters, Inc and Liar, Liar. She voiced Celia in Monsters, Inc and starred as Samantha Cole alongside Jim Carrey in Liar, Liar.
However, since Monsters Inc came out in 2001, she's had a lot of success, especially with voiceover characters. She voiced Madame Leota in The Haunted Mansion, and also guest starred on various television shows immediately after.
She also starred in Out of Practice from 2005 to 2006, in addition to voicing Bonnie Swanson in the Family Guy video game. She had a film called 'Deal' come out in 2008, and then starred in a variety of TV shows [from Drop Dead Diva to Modern Family] from 2008 to 2010. Although Jennifer is not returning for Monsters University, she will be in 2013 in a film called 'The Secret Life of Dorks', and then she also has a film called 'Return to Babylon' set to come out in 2014.