Oddica!

I found an interesting site called oddica. They have great designs from different artists.The good is you can find lots of unique illustrations here. They sell for $20 a piece.

About Oddica (taken from their site):
"The focal point of our company is our Artists. How they interpret a particular idea, and how that idea looks on a shirt, determines whether a customer is going to buy, plain and simple. Our job is to stay behind the curtain and seamlessly deliver the Artist's vision to our customers. Our goal is 100 percent satisfaction, to our Artists and our customers."