This is a topic I know something about
To be honest, I wouldn't say there is currently anybody in CafePress's league when it comes to the Print on Demand game.
There are some up and coming companies, and other companies that do it pretty darn well though. I do pretty well with CafePress and have tried quite a few others.
Zazzle has been mentioned, but you don't get to set your own markups. You only get a 10% (I think) commission, and you don't really get the same type of "store" as you get with CafePress, you just get a spot in their "marketplace". Zazzle uses dye sublimation on their t-shirts and sweatshirts, which has a different feel than the digital heat press that cafepress uses. Some people don't like the "feel" of the t-shirts that zazzle uses, but others don't mind it at all.
SpreadShirt is a newer company that is offering a similar service. They do print on demand using both digital press (dye sub or heat press), and they also do what is called "flock printing", which is a very cool process, where they cut out the design on this velvety feeling material. This allows them to print on dark garments (only one or 2 colors though). You set your own markups, get a store, but the "base prices" are on the higher side. Spreadshirt has operations in Germany(.de), EU (.net), and the US (.com)
Not Print on Demand (meaning you have to prepay for the shirts):
CoShops.com offers a similar service using screen printing and embroidery. They just have a one time setup fee, and varying prices for the screen printed and embroidered products they offer based upon which package you choose. They also have a fully "brand free" shop that lets to work with them to pick out your products and make your store unique.
PrintMojo.comIf you don't mind paying for the stock up front with small minimums (25 t-shirts per design), you can get high quality screen printed (or embroidered) t-shirts and an ecommerce setup. PrintMojo handles the ecommerce, order taking, shipping, warehousing, customer service. You design the t-shirts and market the store. By buying beforehand, you get to set higher markups. For example, if you're buying the shirts at $6 each for a run of 25 shirts, then you can mark them up to $15-$20 each. PrintMojo charges a $3.50 per order fulfillment fee, no monthly fees, no setup, no commitment.
MerchDirect offers a nice fulfillment service for a lot of bands. They also use screen printing, which requires a minimum order to be prepaid, but larger profit margins. They do all the printing in house, and have quite a few ways to customize the stores. They can offer tagging, folding, bagging, as well as custom artwork services.