Google Checkout
Google Checkouts has a launched as a rival to PayPal. Competing with PayPal will be difficult, especially with the eBay integration. That could end when GBuy is released though (a competitor to eBay that will obviously integrate with Google Checkout).
On the surface Google Checkout is more expensive - 2.0% + $0.20 per transaction (PayPal is 1.9% + $0.30). However Google will let sellers have $10 of free transactions for every $1 spent on AdWords. The big disadvantage is that it’s only available in the United States. But that won’t last forever.