They run a weekly contest showing about 5 or 6 fabric patterns designed by their users and then you vote for your fave.
Some recent designs on Spoonflower:
Here is how it works. You upload your design and they will put it on fabric for you. You are not obligated to purchase any fabric - you can keep a portfolio of your designs and purchase when you are ready. Once you have uploaded your design, you will be able to see your fabric with a repeat. The cost per yard (42" x 36") is $18.00. You can order an 8" x 8" swatch for $5.00. They are currently in Beta so you cannot purchase other folks designs but they say that will change once they are out of Beta.
A pretty teacup design on Spoonflower
Don't miss Spoonflower!