So I've been on about 4 different sites regularly and all for about the same amount of time and this is what I've earned in about 2 months without spending a dime. Keep in mind, if you spent all your time on 1 of these sites, or spend money you'll earn much faster. I have a full time job so I don't have the time. I just do this to have some extra cash come Christmas time!
The best is Swagbucks http://www.swagbucks.com/refer/JenniferHiles, in 2 months I've earned 4,030 Swagbucks which equals about a $40.00 gift card I believe. I take the daily poll for 1sb (swagbuck), watch a video and answer a question about it for 3 sb, search the internet and average about 30sb a day and I've found some swagcodes and completed a few offers. Not too shabby for not spending a dime.
The Next is Inbox Dollars, I've earned $13.35 in about 2 months by taking surveys and reading e-mails. Each "paid e-mail" you read earns you about a dime but they add up quick.
Superpoints is probably the 3rd best (in my opinion). I have a hard time earning points on it. I've got about 1,024 points from the Superlucky button, a few superpoints e-mails and I think I completed one offer on it. 1,000 superpoints will get you about a $10 gift card. To be fair to Superpoints, I've spent more time on Swagbucks because they have more options to earn points.
The 4th is MySavings. I have about 585 points on it.I honestly have no idea how i've earned those points but I don't think it is going to get me very much. You can earn points by printing out coupons and redeeming them.
I use a few survey sites like Ipsos an NPD and a few others but I haven't earned any significant amounts there, I typically spend 10 minutes filling them out just to get disqualified b/c I don't match the criteria.