This is by no means a definitive list, but I’ve followed a few RPG webcomics over the years and there are a couple of real gems. My laugh-out-loud favorite is d20monkey by Brian Patterson. He seems to hit the nail on the 4e head; Usually in a NSFW way. His comic mostly follows the gaming adventures of Sam and his gaming group. Some just deal with DnD history or hot topics in the current edition. This is one of my favorites:
http://www.d20monkey.com – updates Mon/Weds/Fri
I just came across Looking For Group recently. I’m sure some of you have been fans for years, but for those who haven’t read it, it follows the adventures of Cale’Anon, the main elven protagonist, and a group of heroes of varying motivations (and definitely alignments!) as they battle to save Kethenecia. It has amazing art and is usually really funny. Some of it is darker, and it is really maturing into a rich storyline. With over 500 pages, it provides an awesome read:
http://www.lfgcomic.com – updates Mon/Thurs
One of the classics that has been around many years is Order of the Stick. This comic has been around since D&D 3.5 and has a deep cast of characters. It follows Roy Greenhilt and his party as they try and save the world! It uses a lot of D&D terms that can be confusing for people not familiar with the game. It tends to have a lot of plot per page and has covered a lot of ground over the years:
http://www.giantitp.com/comics/oots0001.html – updates whenever Rich can
There are more out there, but these are some of the best. Hope you’ve discovered a new favorite, and good gaming to you!