Oh lordy loo - San Fran has WAY too many to list.
a couple favorites -
Geeky Rap -
MC Lars - Signing Emo (He's a Stanford kid, but he's actually starting to get kinda big now. Apologies if you actually like emo - if you don't, enjoy.)
Electronic / Beatboxing -
Kid Beyond (That'll explain what he does.)
And here's his myspace.
Electronic / Downbeats / Jazz -
Run Return (Awesome three man band out of Santa Cruz. That's a link to the "music" section of their site, some mp3's to listen to.)
Metal / Hardcore -
All Bets Off (MySpace)(couldn't find any good youtubes, they broke up a couple years ago. Of the one's on their myspace, catharsis is the one I like.)
Industrial / Rock -
Luxt - American Beast (They're out of Sacramento, and got kinda lame later, but this is one of their good songs. Horrible video though.)
And of course, I've gotta promote my friends' bands (These are myspaces, and they're both metal bands)
Antagony
Hacksaw to the Throat