I've been having fun poking around SixQuestions.com for a few minutes, having been referred to it this morning. You can accumulate points by answering trivia questions, participating in opinion polls, and referring new users. Points can be redeemed for some neat prizes, such as an iPod mini, as well as gift certificates for places like Best Buy, Marshall Fields, Target, and the MLB Shop.
Give it a try. :-) If you sign up and aren't impressed... hey, at least I get points for referring you. ;-)