Just found this thread - very interesting! I was going to mention Inbox Dollars. I don't do any of the extra things (like free trials, surveys games, etc) that actually give the big money. I just open a few emails every day, literally takes seconds. In about 4 months time, from just opening emails (with the other things they offer, you can do a lot better), I have more than $20. Doesn't sound like much, but I literally spend about 15 seconds every day opening the emails. Every little bit helps.
Although they don't pay cash, I also participate in Harris Poll surveys (you've probably heard of them. Harris Interactive is one of, if not the, largest market research firm in the country). You register and put in some demographic data, and you'll get sent surveys which take a few minutes (for me, they always take less time than the suggested time).
Depending on how long the survey is, you get more points. The points can be exchanged for gift cards for restaurants and stores, or magazine subscriptions, small appliances. My sister, mom, and I have been doing it for about 3 years now, and have gotten at least $50 worth of gift cards each. I also have a George Foreman grill I got from them.
Sometimes I'll get 1 or 2 a week, sometimes I won't get any for a month. I haven't turned in my points in about 6 months, and I know I have a ton. I'm just hanging on to them to try and get to the highest tier. Just google "Harris Poll" to find it.