DSF

These are a few sites I've used in the past:

Guru
Found some incredibly talented designers on here a few years back. Worked with folk who have designed for Disney, Universal, West Coast Customs to name drop just a few.

Design Outpost
I enjoy looking through the posts here and seeing what folk come up with, Only used it a couple of times myself and that was for charity work designs.

Bobex

Will add others as I remember them!

Justin

Massive Brain
These designers are first class, great prices as well.

Denis Proulx
This guy did some cartoons for me a few years back, absolutely superb.