I've had the best luck with Swagbucks. I started SB right after Xmas last year and have made about $470 in
Amazon, $100 in Target, and $50 in Paypal.
Next best for me is iRazoo. When I had an active referral I was making a $5 Amazon card every 5-6 days. But they maxed out so now it's only about every 10-12 days.
Also, Let's Break Records -- payout is 2x/month (Paypal. I think they have Amazon too). My goal is to have $10 each payout (that's the minimum) but for this weekend's payout I'm up to $23.
Inboxdollars - I think I started doing it April or May and cashed out in September so 5-6 months. I cashed out at $39 and supposed to be processed on 11/1.
RewardPort - started in June, got enough for a $10 amazon card in September. Haven't received it yet (they say 60 days). I will have enough for another $10 card by tomorrow.
I should add, I took the summer off from most of the sites except Swagbucks.