I do the best with Pinecone. I made a couple hundred last year, did a couple trials for them so got some free stuff as well. Some I liked, some I didn't. IN fact I did one a month ago and we're dying for this product to hit the market - my whole family loved it. They're tough to get into though - even when you find a link or get an invite (in the rare occassions they ask members to send invites out) there's no guarantee you'll get in.
I've done NFO MySurvey for a couple years as well, but I must not be in a very popular demographic since I don't get many real surveys - mostly qualifiers which are only 10 points so are slow to add up. I've made $30 in 2 years and have had two trials.