Here's what I have so far:
Game Time/Cash Cards
Amazon/iTune Gift Cards
Game upgrade serial codes (Such as Collector's Edition Serial IDs)
In-Game high tier crafted items (Armor / Weapon sets)
Game paraphernalia such as game related Soundtracks or T-Shirts
I am hoping to get more public opinions though. If you could control the prize, what would you like to win (within reason)?
Also, does anyone know anything about sponsorship, how to get sponsors, and so on? Information regarding that could be helpful.