One of the funniest webcomics online is The Order of the Stick, written and drawn by Rich Burlew. It's also easily the funniest roleplaying game based comic, funnier than Knights of the Dinner Table and Nodwick, both of which I enjoy.
OOTS is funny on multiple levels. It's humerous both as a comicstrip, as well as with the many injokes that poke fun at the whole concept of rpgs and the people who play them. Things that gamers (particularly D&D players) say at the table are uttered by the characters in the comic-things like "I FAILED MY MOVE SILENTLY SKILL CHECK!" or "Hey! I just got 4 skill points!" which aren't funny in and of themselves, are quite silly when said by the characters. The blurring of the lines between players and characters is what makes the comic so great.
Don't believe me? Go read some of the strips for yourself. The first few strips aren't the best ones, as the comic was still finding it's feet, but trust me, once it gets going, it's one of the few places online that make me actually laugh out loud. If you aren't a gamer (or know one well enough to get some of the references), some of the jokes might go over your head, but there is still plenty there that's funny even without the rpg references.
For the month of September, Rich is also sending the OOTS wallpapers out to anyone who donates to the Red Cross to help out those in New Orleans. All you need to do is forward a copy of your email receipt to him, and he'll get the wallpapers out to you in a few days.