Eddie Izzard is a surrealistic comedian that uses smart humor. Greg Proops has a biting stand-up routine that focuses on the absurdity of pop culture. Mitch Hedberg is a late comedian that many consider to be one of the greats. Margaret Cho and Joan Rivers are excellent female comedians.
George Carlin, Eddie Murphy, Robin Williams are all good comedians. If you are looking for historical ones, you may want to consider such greats as Red Skeleton and Lenny Bruce, who changed the landscape of stand-up comedy forever. Comedy Central regularly airs stand-up specials that feature many different comedians if you want a variety.
Red Skelton, Bob Hope, Carol Burnett, Jack Benny, Bill Cosby, Tim Conway, Milton Burle, Johnny Carson, Richard Pryor, Eddie Murphy, Jay Leno, Phyliss Diller, Joan Rivers and Lucille Ball to name a few.