We’re recommending some ecommerce applications if you’re interested (these two are for Windows servers). There is a product from Early Impact called ProductCart which is simply amazing. They released a new version about 6 months ago which rocks the world. We utilized it on CushionCraft.com, a site that sells custom cushions made to order.
Another shopping cart we’re just beginning to use is called BVCommerce and there are three versions currently (and a whole new release is coming this month I understand which will be .NET as opposed to older ASP). The neat thing about this cart is that it has a feature to sell downloadable products such as software or PDFs.