Most leading universities have graduate programs where the masters and doctoral students need to survey a cross-section of the population to prove (or disprove) a theory. By signing up with these university sites you can make money or earn prizes.
These are usually very interesting surveys and I have participated in experiments regarding my views on race and politics among many other topics. Many of the surveys pay with Amazon e-certificates that you get very quickly after completing the survey (TIP: log into your amazon account and under "your account" add the gift card code to "apply a gift certificate/card to your account". That way there is no losing the email). Others give you a percentage (say 1/10) chance of winning a prize. I have won many gift cards through these lotteries - they usually give pretty good odds!
I check these sites often as they usually don't email about experiments. I say experiments but really it's just reading some material and answering questions - you answer from the comfort of your home and they interpret the results! Here are the ones I am a part of:
Stanford Graduate School of Business Behavioral Lab
UCLA Anderson School of Management Behavioral Lab
eLab at the Yale School of Management
Columbia University Center for Decision Sciences
Psychological Studies at Harvard University
Lewis & Clark College Behavioral Health & Social Psychology Lab - take survey to sign up
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