I have actually used Elance and just been subtle about it (They don't allow porn, but they aren't that strict about enforcement.) They seem to have the best pool of people I've run into.

There's also rentacoder.com, but it's a much clumsier site to use, and in my experience, there's a lot of variation in the quality of the people who bid. On the plus side, they have a lot of protection for the buyer and seller in that they actually handle the payments through their own accounts, and if all the correspondence is done through the site (as required), then they will handle all mediation if there's an issue, and it's quick and simple... so you won't get ripped off. And they are strict about timetables and updates from the coders, so jobs don't languish.

The other one that looks promising, but I haven't used, is guru.com.