Some simple stuff I do myself. For the more complicated stuff I started out with using digital point...but then I switched to http://99designs.com/ and haven't looked back. You get way more submissions so you have a much higher chance of getting something truly good.
We used 99designs just recently for logo work for www.neighborex.com. Was a great experience. Designers were easy to work with. Process was simple and painless.
We used a prize of $500 for each logo. In both cases, it was the highest paying contest on the site when started. In the second case, a $750 contest started soon after, but it didn't seem to impact our results negatively. The cost of running a contest is $39 (it was only $30 when we first used them).
