From personal experience, I can recommend Amazon Mechanical Turk as a website where surveys are usually valid. Mechanical Turk allows individuals to complete small and usually easy tasks for tiny amounts of money. Since the tasks are fast, you can complete lots of them in a few hours, and if you're fast the pay can eventually equal a minimum wage job.
Alternatively, the site Swagbucks rewards answering surveys with, well, swagbucks, which you can redeem on various prizes. I recommend these sites as good ways to slowly work towards a prize, but you're not going to become rich off of them. If you don't mind small earnings and enjoy taking surveys, give them a try and see what you think!