Which debit card offers the best rewards?

I'd have to go with the https://www.paypal.com/cgi-bin/webscr?cmd=xpt/auctions/PaypalPreferred-outside PayPal Preferred Rewards Card. 1% back on all purchases in cold hard cash. To qualify you have to sell a few items on eBay as a Paypal Preferred seller, but it's well worth it for the 1% cash back.

Personally I've had the card for something like 8 years now, and I'm grandfathered in at a 1.5% reward rate. But even 1% is better than any other debit cards I know of, and it's about as good as you can get on a credit card nowadays (see sources). If you're not willing to sell a few items on eBay, or you would prefer non-monetary rewards, http://www.creditcards.com/credit-card-news/debit-card-rewards-1277.php a list of other debit card rewards programs is at creditcards.com.