99designs is amazing - great to work with - helps you out in every way, and keeps the designers on track so you don't have to worry about anything except your design.
I had to extend my contest by a few days due to a death in our family and they were super accommodating and everything worked out great. I can't say enough good things about working with this group and have done on several other designs - all with the same outcome - a totally great experience and design!