Unfortunately, posting names of such sites are not allowed in the forums -- it be best to run a quick Google check for such; to make sure you'll be signing up for a good site, make sure to check as many sources about the said site -- backgrounds, user info, scam reports -- there's a lot of info from the Web one can find to make sure they won't be scammed for their effort and earnings
Remember: always use the search engines to find facts; don't just sign up to the first thing that pops on the search; always find both pros and cons about the site you wish to join -- then, only then, when you do sign up -- it must always go down to a sustainable and secure earning, not a quick-rich method