I have used and had amazing experience with 99designs. You online a basic idea and then you set your award budget, and you get several different artists showing you their ideas, which can than be expanded upon, etc.
Here is a link:
http://99designs.com/promo/20off?noredirect=1&utm_medium=cpc&utm_source=google&utm_campaign=Logo+Design+-+US&utm_content=logo+creations&utm_creative=57701337273&utm_target=&utm_term=%2Blogo%20%2Bcreation&utm_placement=&gclid=COHVl_iUgMsCFc5Zhgodl7IBGA