I recently competed in a T-shirt design contest and it was hard to find a "free to use" t-shirt template that I could use for personal and commercial purposes. SO I decided why not create my own. Went to the store, picked out some blank white t-shirts and created a lighting setup to create as clean of a picture as possible.
Included in the .PSD is each side of the t-shirt on it's own layer SEPARATE of the background. So you can mask out the shirts to paint over them without going outside of the edge of the t-shirt. There is a Front and a Back template of the shirt.
IMPORTANT: This resource is free to use for Personal AND commercial purposes. No need to credit and source back. Enjoy =]