I'm usually not one to promote stuff like this, but I have to get this company its due. They offer an incredible service for NO charge. Some carts of a similar nature go for $200 a month plus a slew of start up charges.
This is an API checkout system that works both with PayPal AND Google Gheckout. I have full integrated it into my HSO sites and it's really a huge improvement over the old "Buy Now" and "Cart" buttons offer by PayPal or Google alone.
The best part of course is the price. But this is a powerful tool and might be useful for some of you in eCommerce. Just wanted to give the company it's props. It's good to still find gems like this.