I use Mypoints. I so far earned $50 in Amazon Giftcards. All I did was search for stuff on their search engine, do surveys, and get points for shopping at Mypoints sponsors shops like Ebay.
^This is why I use a seperate E-mail for online shoping, doing paid surveys, and registering at websites. I use another E-mail address for stuff like keeping in touch with family, and other important things.
It took me a year to earn 25 bucks, but if you shop from their sponsor sites (from their website) they give you back 2-10+ points per dollar spent, so it can take only a few days or months to get 25 dollars in Amazon gift cards.
Been doing paid surveys for a while. As long as you take the surveys to earn cash or points and not complete any free or paid offers (may lead to spam) you should be okay.
I agree if you stick to surveys and don't do paid or free offers you should be fine when it comes to not getting spam. Most of the paid and free offers also have an Opt-out option to not get e-mail newsletters.