HitPredictor is fun for those into testing out new music.
I enjoy it cause I get $5 Amazon gift cards periodically for listening to 10-15 song samples and providing a little review of them of one or two sentences (they will email you when those contests come up, usually weekly on Wednesdays).
They also have contests for $50-100 Amazon gift cards as well as Hidden Song contests for $15-25 iTunes gift cards (I use those to buy the paid iOS apps on BestReviewApp). They limit it to the first 50 people to listen to and review the 10-15 songs for the contests.
The points they give per review can add up fast and be used towards purchasing CDs, DVDs, or entering giveaways for Amazon gift cards, iTunes gift cards, or other prizes.