This startup Questli is giving away free iPhone 4 cases made by Graft Concepts. (as well as other prizes on their website such as ipads and macs but this is an iPhone forum )
There is no catch, just need to download thier APP, Questli (itunes download link)
You will need the invite code "TC2011" from the Tech Crunch Article released today showing how the app was just officially launched, and these prizes are part of the promotion!
INSTRUCTIONS FOR THEIR BLOG POST: