I am so excited to see this service called Spoonflower where you can design your own fabric then purchase some of it for a reasonable price! The service is super-easy to use and a yard of your fabric is only $18 (you can get up to 3 yards at once). I'm all set for my current quilt and I'm really not a designer so I haven't created a fabric and placed an order yet myself, but I could definitely see doing this in the future. For a service to be so easy to use and the cost to be so minimal, I don't see the down-side in trying it out.
You can also explore recent fabric designs others have created, which is a feature I love. While you can't order others' designs directly from Spoonflower, many of the creative fabric designers have links listed to their Etsy stores where they are often selling their original fabrics. Check it out!