SonicShack desktop T-shirt designer
Design Studio from Sonic Shack makes things a bit more interesting. It's a bit like CafePress but on your desktop and more fun in my opinion. You can upload your own photos or designs (JPG, PNG and GIF files), and add text and clip art from the stock library. There is even an entire category for skulls in the symbols section of the library.
There are also a lot of font choices and options to rotate and flip images to make things more interesting. To use the free version and save your design you have to enter your email address and a password and name the design.
It's nice to have this in a desktop application. It speeds the upload times if you are taking things directly from your own drives and you can use it without worrying about it the web is going to be slow that day. I found it relatively intuitive to use so there was no learning curve.
You can print shirts for as little as $18.50 each, which, for a totally customized, one of a kind shirt is not too bad. You can also add the Sonic Plug-in to your website and sell custom shirts and make a profit as well.