Well, I haven't done many offers in a while, but these all have credited me fine:
Global Survey Group
Lucky Surf
Free Listerine
FREE PC Magazine
Venus vs Intuition
Nielsen/NetRatings
Ebay Shopping Spree
Bid4Prizes
The Final Payoff
NPD Male Survey
Win a Razr 2
Free Fly
Mystery Shopping Rewards
Win A Nissan
Favorite TV Mom
The Napster, Blockbuster, and Netflix free trials are also great CC required offers that don't cost you anything.