I used Elance and it worked pretty well. Be careful though. I posted project specs and had about 15 bidders. I found out once development was done, one of the bidders who didn't get the job liked the idea so much he wrote his own version, based on specs I provided for the bid. He even used the same name. So, on the appstore, I had to rename my app AND had a competitor immediately. Luckily, Apple and Elance took care of it and his product was removed.

I really liked the way elance gets you in touch with the developer and handles payment really well. Also, the communication system worked well. Would do it again.