I beg to disagree. The best survey sites all maintain your privacy and will not send you any spam. Among these I would include surveysavvy, ACOP, globaltestmarket, NFO, NPD, opinion outpost, Greenfield, Ciao, Pinecone, to name a few.
A few which has been known to send some spam mailings are Survey Networks, Panda Research. But you can avoid them by carefully choosing what to tick while signing up and if necessary using a second email.
Also never pay for getting a survey database, it is all free. Never pay money to the likes of surveyscout. Some free databases like survey-club are also good spammers.
I have been enjoying doing online surveys for some time and in my experience they are good enough to give some good extra money. To maximise your earnings you should join with maximum possible sites and complete all your profiles in each sites.
If you like, a good free survey resource is
http://www.internetpaidsurveys.com