PineCone Research: This site is pretty exclusive, you have to wait until they're allowing people to sign up in order to join. I really like this site though, because you get paid $3 for every survey. That's not too shabby. Also, there are many chances for you to test products. I've tested things like toilet paper, shampoo, and food products. It's pretty fun.
SurveySpot: SurveySpot is a pretty generic site. I get tons of emails from them, but only complete a few of the surveys. You get awarded points, and once you have 1000 points you can redeem them for a PayPal payout, and more recently gift cards to some online stores like Amazon, Sears, and Overstock. The surveys vary in length and difficulty and payout. But each survey you start gets you a drawing into a quarterly sweepstakes (a very popular feature). (Note: It sounds like some people have problems with getting their rewards and having their questions answered by SurveySpot's customer service. I have never had this problem however, so I feel I can recommend it)
Synovate Global Opinions Panel: I'm fairly new to this survey site, but so far I like it. I've only been a member about two months, and I just got my first $5 payout in the form of an amazon.com gift card (which is my payout of choice). The surveys are kind of few and far between, but pay pretty well. Also, the site is generous and often will give out point gifts. There are several different gift cards you can choose from when you get a payout. This panel also holds a monthly sweepstakes. Click here for a list of gift cards
MySurvey: This is a another good site for surveys. You always get at least 5 points per survey, whether you qualify or not to finish it, which is a nice feature. This site has tons of different prizes to choose from, not just gift cards, which makes it unique. They have everything to choose from : baby and kid items, electronics, home and house ware items, and travel vouchers. An amazon.com gift card will run you about 1100 points on this site.
J.D. Power Panel: Yes, this is that J.D. Power, but you don't just review cars for this panel (although I wouldn't mind testing them for free!). I have found the surveys here to be few and far between. I have been a member about 2 months and have made about $15, but I need $25 to cash out. I like that this panel doesn't use a points system, it straight up tells you how much cash you have from them. You can cash out with gift cards or PayPal or you can make a donation to one of several charities.
NPD Online Research: This is one of the first sites I joined before I knew much about any of these. If I knew then what I know now, I probably would not have joined. I do receive a survey every week that usually consists of the same questions. From this, I earn about 25-100 points, which you then use to enter raffles. The raffle prizes all sound really nice, but I have yet to win anything, and doubt my chances for the future. Because there is no definite payout, I would not really recommend this site, despite the ease of it's surveys.
Ipsos I-Say: This was another one of those first sites I joined, and apparently I let it go lax and no longer have an account here. They never sent me an email when a new survey was ready. However, I did fill out about 5 surveys through snail mail and earned a few bucks from them. As far as I know, they are a good company with good rewards, but if you're like me and won't ever go there without a reminder email, this may not be the panel for you.
TruePanel: This is an interesting panel that I am fairly new to. The thing that makes this site unique is the fact that a lot of the surveys require you to have a webcam. There are a lot of focus group style opportunities here that can be completed from the comfort of your home. There are also some studies where a phone call to you is required. I haven't quite got around to registering my webcam and phone number, so I haven't had the chance to do much here. Also, it looks like they only have gift card payouts to 3 different places: Amazon, Starbucks, and Endless Shoes.