I have joined several panels over the course of the last year. The ones that have been most influential are Inbox Dollars, Send Earnings, Ipsos, and Mommy Talk Surveys. With Inbox Dollars and Send Earnings they have cash offers, that give you money back in your account for buying products that you would have bought anyway. With Ipsos, I have been able to test two different products with them and have received compensation. Also if you do not qualify for a survey, you still earn points. You can cash points out for Paypal payments which is nice. Mommy Talk Surveys is the same with the cashout although you do not earn anything if you do not qualify for a survey.
An example of a cash offer is that I wanted to join the Disney Movie Club for my four year old son. I got six movies at the introductory prices. Inbox Dollars credited me $10 dollars back and so it was like I got those movies for $23! They also have offers from companies like Wen Hair and Proactiv, so if you are thinking about getting either of these join Inbox Dollars or Send Earnings and get cash back!
I will leave links to each site, if you are not yet a member:
The widgets for Inbox Dollars and Send Earnings are on the right side of the blog!
Leave your email for Ipsos and I will send you an email invite!!