The shirt builder has many options, including poses, logos and nameplates. You can move each item around on the graph to your liking. It's almost too customizable for me -- too many options. Some of the tools are a little awkward, but I'm assuming that will be ironed out soon.
PrintWarcraft gets its info from the Armory, so your character has to be at least level 10 in order to be able to print it. And just like the Armory, sometimes changes you make to your character in-game can take a while to show up. If you create an account, you can keep screenshots of your characters. But these screenshots are not directly linked to the Armory, so if you change your character's look and want to print that instead, you need to create a new screenshot linked to your new look.
PrintWarcraft.com also offers personalized mousepads and posters. If you're looking for something to replace the customized WoW product hole left by SwagDog, this online store should fill it.