I've been on a serious stand-up comedy run for almost a year now. There are so many amazing guys out there, that it's hard to pick a few to list. However...
Great Comedians:
Joe Rogan - Watch his live special from '05 or '06. It's brilliantly thought out, hilarious, and honestly one of the best stand-ups I have seen.
Brian Regan - How do stay that funny all the time and never curse or say anything that couldn't be said in front of a grandparent or child? He's amazing. Watch or listen to "Stupid in School" and "lousy in Little League" (about 5 mins each). Then watch your next 6 hours waste away as you download clips.
Louis CK - see above, he's awesome
Lewis Black - If you can handle his intensity, the guy is awesome
Ron White - I hate the blue collar tour with a passion, but Ron's original stand up was priceless and consistent.
Dennis Leary - Believe it or not, I am putting him on here. Forget about "No Cure for Cancer" and go find "Lock and Load". The first 15 minutes are terrible because he is on way too much coke, but once he relaxes it is priceless.
I'm missing a ton more.
Newer Guys, and ones I have seen on Comedy Central Presents:
Dov Davidoff - Amazing, insane, and if you can find his older ones, even better
Hari Kondabolu - Looks not funny, but has great material. "What kind of a family needs a hybrid SUV? Well, I am an environmentalist, and my husband is a giant douchebag."
Billy Gardner
Nate Bargatze
Josh Sneed
More to come when I remember them, but these guys are all great