If I wasn't clear eough about the poll, I meant a poll on top of a thread. People can vote once identified or anonymously. The problem is people can also see how the results go right away.
SSS is right, its only hidden until you vote. Otherwise the poll is pointless since the polls option wasn't create for contests solely. So we might have to go with the public voting.
We can do multuple vote, and ask people to choose 3. Except we can't garentee that people to choose exactly 3. Unless a mod can see members' votes and check. But it will also be time consuming
I know I've seen it done on MH, the hidden poll results thing, even after you've voted. Both MH and MS are powered by vBulletin, so I'm pretty sure there's a way. But coming from someone who has only ever started one thread, and it was a release, it's possible that I may be wrong.