Online surveys are both paid and free, depending on the website. There are legitimate websites out there that will pay people to take surveys and there are also websites that will ask for people's opinions with no payment as well.
Pinecone Research, American Consumer Opinion, Opinion Outpost, My Survey and iPoll are examples of online organizations that will legitimately pay people to take surveys. Some of these websites are by invitation only, as to keep the amount of accounts at a manageable number. These websites may also ask users many personal questions initially because the surveys are typically for marketing purposes.