If you buy at Storenvy, I will be the one shipping your items, so this should be your first choice! ;)
This is where I sell my comic books, and all the prints and postcards you can also buy at conventions.
Society6 is an US-based company selling art prints and merchandise. They often offer discounts and free worldwide shipping, so check with them occasionally for great deals. Apart from prints, I sell fun things like here phone cases, pillows, and mugs.
Redbubble sells art prints and merchandise. Their items are similar to those offered at Society6, additionally they sell travel mugs, pouches and posters.
Deviantart offers a small selection of my paintings as prints on paper, photo paper, and canvas.