Many of the options are surveys. One really cool one is the american airlines elite challenge. Challenge (AA - FlyerGuide Wiki)
I'm trying to see how many american airlines I can get for Mike so he will have as many miles as me. Maybe we'll take an anniversary trip (who knows if it will be our 1 year or 50 year-not sure how fast I can get miles).
Oh & none of these deals are shady. It's all legit stuff. I wouldn't give them your primary email, because you will often get hit with spam.