XKCD: Won't bother linking, you can find it about four times in the first page alone.
Giant In the Playground: D&D based webcomic in the creators own settings.
Takes digs at basically every trope and cliche commonly found in RPG's, subverting averting and sometimes playing them straight.
Darths And Droids: What if Star Wars were an RPG game?
Almost finished Episode one, I think the plan is to go through all six.
Ctr ALT Del: Again, no link. A love / hate relationship with this one, as a recent arc has hit a lil too close to home (Work out which one at your own leisure. Don't comment, I'm not liable to take it well) and where it's leading has hit me again.
That, and it flat out sucks some days.