Harold Schmidt - by far the best German comedian i've come across! He's like the German Letterman (but not as good as Jon Stewart).
The hard part is that your German must be really good to understand him, not only that, you really have to know German history/current events/slang/feelings (in short, actully BE a German) to really appreciate his humor. Fortunately I have a German boyfriend who can explain what I don't get
He's actually quite celebrated in Germany - even has guest appearances during the biggest football games.
Definitely worth a watch! (Especially if you think Sponge Bob is funny...)
http://www.schmidt.de/index.php3