There is a new kid on the block to compete with companies such as PayPal (owned by eBay).  Google Checkout has launched, which allows a shopper to purchase items from websites that use Google Checkout without having to expose thier information to the sites.  Google is promoting this as the secure way to do online commerce.

They also have integration with Google Adwords so if you use this on your site and spend money with Google AdWords, you can process $10 worth of sales for free for each $1 your spend in AdWords.

Bottom line is mostly, 2% of sale + $0.20 transaction fee.  This can still add up to quite a bit!

https://checkout.google.com/sell?promo=sbop