Contest musing

So I’d like to do some contests–either for the Corvis Rebaine novels, The Goblin Corps, or both–that involve either the creation of artwork, or the the translation of some of the characters into people’s favorite role-playing games. But I’m not comfortable with the idea of a contest that asks dozens or hundreds of people to send me files via e-mail, since the chance of a virus (even unintentionally) is a little high for my tastes.

So, I’m asking for suggestions. If I were to do such a contest, what are some ways I could arrange to get the files to me without risk of infection? What sorts of services, if any, exist for such huge numbers of file transfers that won’t cost me much (if anything) out of pocket? (Said services have to include trustworthy virus-detection on the server side, of course, or there’s no advantage to using them over e-mail.) What other options might I have?