The best of the survey for United Miles batch right now is Opinion Miles Club. Big thread on it here:

http://www.flyertalk.com/forum/miles...ng-survey.html

It can get annoying to get bounced from a number of surveys in a row with them, but they normally credit to your account instantly (and at worst within 48 hours) unlike MyPoints, Opinion Outpost, or e-Rewards, where you generally have to build up a fair number of points before you can transfer them into a miles program. You can also pick up about 500 UA miles a year from e-miles.com by clicking through a couple of spam e-mails a month.