Early bird hotel reservations are now available for Comic-Con International in San Diego this July. These are mostly for hotels some distance from the convention center and some of them are in San Diego only on a technicality. But they have rooms and they're not as expensive as the lodging you might (might!) later be able to secure at closer places. For info, check here. Me, I'm thinking of going into one of the rooms where I host panels and setting up one of those tents that homeless people live in.
And here's a page from the good folks at the unaffiliated-but-often-helpful San Diego-Comic Con Unofficial Blog. It'll give you a general overview of how housing works for the big event.