I have a full studio with Profoto strobes. If you need some more contributors, let me know.
Some other thoughts:
- I think you'll grow out of Tumblr and Dropbox real quick (I'm already seeing Dropbox errors)
- Give people an option to "buy out" an image from the set. For, say, $100 someone can license exclusively an image and it's no longer available.
- Include some Photoshop files that place a screen shot on the image and apply the proper perspective/warping. People can then just drop in their screen shots.
EDIT: Here's a quick-and-dirty example of a PSD with a "placed" screenshot that is adjusted properly to fit the screen: