Yes, it is an issue because Dane cook became popular.
However, thats likely how people found out about it. If he wasn't popular, what do you think the chances are of anyone at all noticing he's been steeling his material? Not very high, as either a) No one knows about it, or b) He's not popular because people figured out ahead of time he was stealing jokes and has been shot down for it by the people, meaning theres no need to go after him as the works already been done. Otherwise it would be like kicking a dead horse.
Anyway, more on topic.
My personal Favorite Comedian is Lewis Black. Black on Broadway was all sorts of hilarious, especially the bits on Water.
Mitch HEdberg was also a genius. I love the PCP and the loud music bits he does.
Honorable mentions to Patton Oswalt, Kevin Smith, the guy who did "Behind the Pale", Dave Chappelle, Katt Williams, Lisa Lampanelli, Sephen Lynch, and this guy.
YouTube - There's always whiskey - Eric Campbell