CafePress is fantastic site and business model. I'm not sure how well they're doing...but once they reach a tipping point of volume, they'll do great.
Their products are a bit expensive ($11 cost for a mug), but their value proposition and ease of use makes me forget the price, just as I forget that Buy.com has cheaper books than Amazon.com.
CafePress allows you to place any image on t-shirts, mugs, mouse pads, etc. You can see what it looks like online immediately, and buy it at their cost. Or you can set your own price for that item and put them in a custom online storefront for others to buy.
Here's my family of family products. My kids love this stuff. No customers yet, except me. :-)
BTW, I created charactures of our family to give our kids a sense of family pride and kinship to the "Decker Family". Kathleen Doherty did a fantastic job creating these at a great price.