In descending order
Eddie Izzard - Specifically "Dress to Kill", I could watch that show forever. Few people can make the funniest stand up ever out of a subject like history. "Glorious" is also pretty good, goes downhill from there.
Jim Jefferies - "I swear to god" is probably my most-watched stand up of all time. The latest one isn't as good tho.
Mitch Hedberg - Better in short 10 minute bursts than the full 90 minute CD IMO, but those are some mind blowing 10 minutes. Just hearing him say the word "Duck" cracks me up now.
Past those 3 it get's pretty interchangable. Honorable mentions are Eddie Murphy, Dylan Moran, Anthony Jeselnik (Funniest Dane Cook impression ever!), George Carlin, Dennis Leary, Daniel Tosh, Geoff Keith, Timothy Young and Whitney Cummings.