Here's another Vividence invite from Microsoft to evaluate four of their community sites for a $15 Amamzon GC. You should get a popup from Microsoft's homepage asking if you want to join, but if you don't or clicked 'cancel' earlier, here's the link:
LINK
I signed up this afternoon and had an eval invitation waiting for me when I got online tonight. Completed the eval and immediately got the GC by email. It'll go nice with the $40 GC Vividence gave me last week for doing a Compaq/IBM eval!
I like Vividence as well. It's one of the few survay sites that actually pay me well and often. YMMV, since it is luck-of-the-draw based on your demographics, but I've earned over $150 worth of Amazon GCs over the past 1 1/2 years by signing up with them and evaluating websites.