The first merchandise site that I tried out was CafePress.com. It was great to upload my images and see them virtually as they would appear on a t-shirt, sweatshirt, messenger bag, coffee mug, buttons and more. I created a store and upload my art very sure that my friends and family would be so happy to buy my products. I also figured it would help me discover what designs were popular.
The downside to CafePress was that the base price for each item was so high, even charging 5 dollars over the base price for an item made it expensive. The base price is how much it cost for the single blank item without your design. I realize that one-offs are always more expensive to produce but I think they could lower their base prices. The second part I did not like was the quality of the t-shirt printing. This may have changed in the past few years but in 2008 they were using the iron-on printing for the graphics. This technique does not hold up in the wash, it fades and cracks and peals off.
I have recently joined and plan to order some products from some of the new places below to see if their quality is better. If you have ordered from any of theses sites pleas let me know what your experience is.
http://www.zazzle.com/ (not a member yet)
The best place to sell handmade original items still remains Etsy.com and Fine Art America. Fine Art America cost much less than Etsy but has less traffic. Etsy has 6,992,268 unique visitors a month and Fine Art America has 530,395.