The first is Megatokyo. This is probably one of the best known web comics around so I don't think it would really be useful me trying to explain it more than simply "two American "fish out of water" stranded in Japan".
This is also one of the very few cases I've seen of an American (as far as I can tell) artist doing a comic in manga style and it actually working. Part of that is probably the story being set in Japan; but also it seems that he's got a good grasp of how to balance the mundane and the fantastic that I've seen in some of the manga I've particularly enjoyed reading.
Gaming Guardians took a bit of getting into. It's a good comic, but in its huge archive it doesn't seem to have any section breaks for the characters (and the archive reader!) to stop to catch their breath. I did, eventually, find out that the secret to enjoying it is to not worry about not quite knowing what's going on. Everything important is going to get explained once it's necessary for it to be explained. Once I understood that, it was good fun reading; I just didn't bother wondering who all the cast were.
As for the actual plot... it's a bit difficult to explain, but, basically, it revolves around a group of dimension-hopping watchmen / fix-it-people who ensure that Nasty Stuff doesn't get into games (generally of the video / role playing type). Or, to paraphrase one character, they're there to roll dice and kick arse. The story's structured fairly much like a soap opera; there's always some twist waiting to happen. The main character's a bit of an author avatar; other regulars include a smart-arsed robot, an invulnerable "tough chick" and a couple of Minotaurs.
But what probably impresses me the most is that this is the third of "Graveyard Greg" 's comics I've read, - the three of them being in vastly different genres - and all three of them have been very good reading. I will have to go on a hunt to see what else he's written at some point.
And some quick notes on other comics I've read:
Buttercup Festival is distinctly odd. Very nicely drawn pen and ink backgrounds (often of landscapes) each contain an oddly shaped creature who comments, sometimes on the scenes but more often off at a (sometimes surreal) tangent. This is one I particularly liked.
Crossroads: Read and enjoyed.
Footloose: Part adventure story, part completely absurd but good fun all the same.
The whole point of Three D Comics seems to be that its art consists of 3-D renderings of its characters. An interesting idea, but there doesn't seem to be a whole lot else to it. There's a plot, but it's confusing and the absence of a cast page or much in the way of explanation of the background to the story doesn't help.
Wolf (not to be confused with another comic of the same name): Read and enjoyed.