My favorite's George Carlin. I can know every line of one of his bits, but he still cracks me up. Great delivery, great choices of subject matter. I'll miss his insight these years to come.
don't think I could pick just one but Christopher Titus, George Carlin and Larry the cable guy to name a few
Sean Lock http://www.youtube.com/watch?v=SklxlxQ324c enjoy!