I've been doing contract work for three years; 95% of my work has come from Craigslist or from referrals from people who I connected with through Craigslist. You have to wade through an incredible amount of junk, but the volume on CL can't be touched anywhere else, and there
is good stuff in there. I look in computer gigs and I also periodically post an abridged version of my resume in the resume section.
Other places I've found stuff include Dice.com, 37signals Gigs Board, Freelance Switch, and AuthenticJobs.
I get a lot of recruiters for contract jobs contacting me through Dice, my resume post on CL, and my blog. That might not be the kind of thing you're looking for, but it doesn't hurt.