I love 99Designs.
I have friends that like Fivver *or* Odesk and things like that.
But the PROBLEM with those sites is that you only get ONE designer with one viewpoint.
With 99designs, you create design CONTESTS in which multiple designers compete to win your design. It is super easy to use. I'm always amazed at the different ideas you get when you have multiple designers.
Once you have some designs, you can offer inputs on each design and improve it to your liking. While you are doing that you can send the designs out for polls to readers or friends – which I did.
I've used 99designs to create the RV52.com logo (Fitty) and a book cover. I'll put them both here.
Anyway, I highly recommend 99designs.