Allright, here's my general list of recommendable web comics:
High Fantasy
Dire Destiny - drawn in a distinct style, yet very nicely detailed comic with a well-told story about old and new gods. Updates every two weeks.
Chronicles of Garas Classic D&D fantasy stuff with elves, dwarves, scantily clad rangers and necromncers and two types of lizardmen. Very nice artwork, good story. I hope the artist switch won't hurt the comic, but the new guy's stuff seems in line with the old guy's in terms of quality as well as style. Updates Fridays.
Rise of the SentinelsA D&D-ish fantasy comic about a peasant boy who is chosen to be a central element in the struggle between two ancient races. On hiatus, sadly.
SciFi
Monica Furious One of the two decent cyberpunk-y webcomics I found so far. Updates every time easter, christmas and thanksgiving fall onto the same day, but it DOES update. I think.
BFX 2A cooperative between two comic arists and the other really nice cyberpunk-y webcomic out there (that I know of), it's got great artwork, nice characters, good stories and updates every 2 months, if you're lucky.
Alpha Shade has already been mentioned, but here it's again, for completeness' sake. Updates about weekly.
Marsh Rocket is a comic that takes place on a colonised mars. Nice artwork, even if the colours take a bit getting used to. Updates every other week.
VOLG A somewhat odd but very well drawn Manga, taking place on an odd world in th edistant future where, among other oddities, giant albatrosses are a popular way to get around. Updates irregularily. The english translation is bumpy.
Other
Cown Samurai, A comic that is about as noir as webcomics seem to get these days, is about bushido, mobsters and a clown who moonlights as an assassin. Seemingly discontinued.
Dr. McNinja Well drawn and utterly hilarious. Updates often.
The Pet ProfessionalNot quite up to the rest in terms of artwork, but pretty funny to read.
Elf Only Inn A classic restarted and with better art than ever, this comic will seem very familiar to anyone who plays online, whether in char rooms or in a game world. Updates twice a week, at least.
Biozoic A web comic without words, but lots and lots of violence. Basically, creatures eat or otherwise kill each other. Nice monster design.