Software would rock. If you gave away legal copies of Photoshop, Premier, TGP submission software, TGP scripts, AVS software, etc. it would come in handy for people to use to get MORE traffic to your sites.
Plus, you might be able to get some of the software programmers (obviously not Adobe, but maybe some of the TGP script writers and such) to sponsor your giveaway in exchange for the advertising and you wouldn't even have to pay for it.
Oh, and you could do the same thing with content. Contact some content providers and ask them to sponsor your giveaway in exchange for advertising and then you could give away content packages. Maybe they would use the content they won to promote you even more.