Really, the title says it all, just go to the SIGGRAPH site and reserve one now. Even if there’s only a 5% chance you’ll go, book one anyway; you’re not charged until after July 9th and can cancel at any time. When you cancel your room will almost assuredly be snapped up by someone else. I’ve lost count of the times people have told me, “well, I had to stay 3 miles outside the city, next to the freeway”—no, you didn’t, you just had to book now.
Me, I like the Figueroa for walkability and its bar & pool area (plus it’s next to the brand new HQ hotel this year), some people like the Holiday Inn as it’s generally less funky, is even closer, but across the wide street. Neither is a bargain this year; the Ritz Milner is a bargain and is walkable, but has some downsides. Everything else is about in the same $143-$199 price range except some of the more distant hotels (Kawada, Wilshire Plaza), but of course these have shuttle service. See the map, and prices are listed on the second page.