I came across this really cool resource today called LiveSurface. It is like a stock photography site but for product, environmental, and packaging mock ups in both isolated and real life situations. While the price per image seems kind of high ($29 per image) you not only get the image but also a photoshop file with the usable area pre-masked, lighting effects added, and perspective applied automatically. They also have tutorials to give you step-by-step instructions on how to do various effects within the templates. Let me know if you guys ever use this resource. I'm curious as to how well it works.