eBay has a beta-test going which gives you 2% of your eBay purchase paid for with a PayPal account. You accumulate eBay Bucks for three months, and then have a month to spend them on any auctions you win. You have to be invited, and I'm not sure how that is handled, but I have participated for the past three months. Got over $25 back to spend in the next month. I hope it continues.

Here's info on the program:

http://pages.ebay.com/rewards/faq.html