I have worked with quite a few checkout systems and eCommerce platforms.  Are there certain kinds of interfaces that convert sales better than others?For me there are really only two questions:SSL self hosted vs. 3rd party checkoutfor SSL this requires an SSL certificate and secure website routines to handle a credit card.for 3rd party, there is PayPal, Authorize.net, and GoogleCheckoutSingle-Step vs. multicheckout see: step two on this pageSingle-Step seems easy enough, but does it convert better?multicheckout can get convoluted, but with a progress bar does it help the user convert?Hopefully this will focus on the four possible answers given either/or answers to the above. 
What is the best kind of checkout system for a website?
https;ecommerce;paypal;google checkout
I would argue the checkout is the most important component of the ecommerce platform. If your users get confused, they WILL abandon their carts. There are two things to consider with a checkout.StepsThe checkout process should be at most 2-4 steps. I've seen carts that have as much as 10 steps to checkout... a death trap for any business. Each step should be obvious what is required of the customer and obvious where to go next. For a test on what is obvious, stand 6 feet away from your computer screen. What you can see 6 feet away, will be immediately obvious to most users. Required InformationThis is a balance with Steps. If you have a one page checkout and loads of required fields it can be confusing. Ideally, you only need Name, Address, and Credit Card information, how a cart handles collecting this is vastly different from cart to cart. Also, can a customer go back and edit his information from other steps without losing all the entered data? That's big.It all goes back to the old mantra Don't Make Me Think. If you have to search for a link or what to next... your customers will have a tougher time than you.