[girasquid]

I was after people who used iTunes to listen to their music for Beathound (http://beathound.com), so I created a survey asking them about their listening habits and offered a $100 iTunes gift card as a reward in the hopes that folks filling it out would self-select based on how much they cared about the gift card. I posted a link to the survey in a handful of survey-oriented subreddits (/r/SampleSize is good) as well as some specific ones (like /r/music and /r/itunes).

I had them leave their email if they wanted to be notified of the survey results, and then when Beathound was ready to go I sent them a nice email that said "Thanks for filling out my survey! You didn't win the gift card, but [here] are the results, and [here] is what I built using them."

I had a terrible time giving the gift card to the person who won it, because they were in Australia and I'm in Canada - if you're going to give something away for your survey, make sure that you can easily do it internationally.