Louis CK is an interesting example of an artist who has grown. His stuff from 20 years ago (that I've seen, at least) was really bad; it was timid and boxed in by convention, which is death to comedy. Somewhere along the way he obviously said fuck it and started telling the truth more directly and provocatively. And that is how lead is transmuted into gold. Funniness is almost a side effect.
Now he seems closer than anyone working in this area to Lenny Bruce and Bill Hicks territory (if anybody's closer, I'd love to hear about them) with at least a shot at equalling them, which would be amazing.
In this video [1], he explains what happened "somewhere along the way". TL;DW: He failed at being a successful comic by telling the same jokes for 15 years, then got inspired by and emulated George Carlin, threw everything away and started over.
His story is not only inspiring, it transcends comedy. The idea that a mixed but passionate reaction is better than a lukewarm one applies to startups as well as entertainment.
I like Patton Oswalt and also Chris Rock, but both have gotten schtickier as time has gone on.
The same undercurrent of respect for comedy- as- craft runs through Patton Oswalt's stuff though, which even if that doesn't automatically make him Bill Hicks, I still very much enjoy hearing about.
Louis CK is also excellent live; if you're seeing him live in a given year, you're basically guaranteed to be getting an entirely new show.
Greg Proops is fantastic, but not everybody will like him. But he definitely ventures into less funny and more socially conscious territory with comfort and without pretension (ok, maybe a little pretension).
Doug was on Louie this season and did an amazing job. He seems to be a comedian's comedian--his name comes up in interviews all the time when comedians are asked who's their favorite among their peers.
Part of Doug's persona is an utter lack of self-respect or self-worth. I think his unapologetic lack of genuine insight into some of the issues he discusses portrays an universal and uncompromising policy of total honestly which is very powerful.
Much of his performances involve veering sharply from some relatively considered insight into the human condition to some completely unnecessarily graphic tirade against a trivial aspect of his everyday life, with absolutely no break between them. In many ways it's as much performance art as it is standup, he has a more fundamentalist attitude towards attacking sacred cows than any other comedian I can think of.
Also I'd add that his more recent work is considerably improved on a lot of his slightly more incoherent stuff from earlier in his career. His "No Refunds" DVD from 2007 is a lot more focused and better paced. Check it out.
Now he seems closer than anyone working in this area to Lenny Bruce and Bill Hicks territory (if anybody's closer, I'd love to hear about them) with at least a shot at equalling them, which would be amazing.