Well, since I do blog about it, I guess I have to weigh in.
In no particular order:
My Coke Rewards
Disney Movie Rewards
Pampers points (only because they are so easy to get; the prizes suck)
Starbucks
Listia (to earn points to trade)
Cash/Gift Card programs
Inbox Dollars
Mypoints
Checkpoints
Shopkick
swagbucks
Mike