Easy Basket is a very original shopping cart application which enables us to sell items inside any web page without any big code/structure updates.
Once installed, the products and basket can be inserted into any part your web page where they will start functioning instantly.
When an item is added to the basket, a sliding + Ajaxed basket can appear to to show the total price and display the checkout options. Also, you can drag 'n' drop a product into the shopping cart as well.
It is possible to enable the user to choose various details about the product like the "color", "size", etc. and they will be shown in the basket as well.
EasyBasket supports PayPal and Google Checkout where their details can be mentioned inside a simple "settings page" provided.
And, the core comes as PHP and ASP, so, you can choose the one that best suits your needs.