3dcart is a complete online store and website solution. Service includes shopping cart, domain name, email accounts and web hosting with dedicated IP address. Free store templates, no graphic design or programming skills required
Cost: Starts at $19.99 per month for everything.

Mals-e is a free shopping cart system that allows you to add your own buy-now buttons to any webpage, customize your shopping cart pages and start selling online. Sell as many products as you like, Mals-e can handle all sorts of transactions, including selling downloadable goods (like ebooks)  and accepting donations.
Cost: Free. Premium accounts start [...]

1ShoppingCart.com provides you with a powerful and versatile shopping cart system loaded with all of the essential features you need to make your online venture a success!
Cost: Starts at $29 per month

X-Cart Pro is an advanced shopping cart software, designed as online marketplace to enable multiple sellers/vendors to offer their products in one online store, X-Cart Pro incorporates all the features of X-Cart Gold shopping cart software and, in addition to that, provides advanced Multi-vendor functionality. Every seller can manage his/her separate inventory, customers’ wish lists [...]

X-Cart is template based software with open source code. This means you can modify the look & feel and functionality of the shopping cart the way you need should you require any business specific features.
Cost: $229 one time fee
Supported payment types: E-Gold, NetPay, PayPal, 2Checkout, AuthorizeNet, Google Checkout, LinkPoint, PayNet, PayPro, WebCraft plus dozens more.

osCommerce is an open source, PHP shopping cart that makes managing an online store easy. osCommerce allows you to run a web store without having to work with HTML (HTML knowledge required to make changes to the layout). The store has an online admin area where you can add/edit/delete products and print packing slips easily.
Cost: [...]