Recently, I have been searching around for scripts/platforms and ways to build E-Commerce sites on the go. When it comes to E-Commerce Sites and Platforms there are many things to be taken care of when selecting those platforms for your business and website. Some of the things that are critical in the Ecommerce sites are Billing, Shipping, User Management, Catalog Management, Catalog Browsing, Checkout, Mobile Commerce, Support Community, Marketing etc.

So, Now I am going to categorize the platforms or ways to build these E-Commerce Sites.

1. Magento - Magento is a customized version of OsCommerce. It is designed by a company called Varien. It comes in two editions Enterprice and Community (Free) . It has got many features which are very effective and gives the edge to this ECommerce Platform. Some of those are , Marketing promotions and Tools, Search Engine Marketing, Analytics and Reporting, Catalog Management, Good Supoort Community, multi-lingual, Customer Service, mobile commerce (iphone optimized). you can find the complete list here.
2. OsCommerce – OsCommerce is one on the oldest Ecommerce Platforms out there on hte Internet. Its has a huge audience and support base. Its open source/free.  Some of its features includes it supports unlimited products and categories, Multicurrency support, Support for physical (shippable) and virtual (downloadable) products, Object oriented PHP backend, Web Browser Install and Plugin support. You can more information about its features and versions here.
3. ZenCart -  Its also a shopping ECommerce Solution that is very famous among companies to show in and sell their products. Its Free and open source. Some of the feature include easy installation, multiple customer modes, unlimited category depth, multiple sales and discounts, multiple display modes, User frontend is validated to XHTML 1.0 Transitional, Integrate with phpBB is a high powered, fully scalable, and highly customizable Open Source bulletin board package. Meta Tags keywords and descriptions can be controlled at the per-product level.
4. WHMCS - Its a pretty specialized solution for those who want to start their own web hosting, domain registrations companies or websites. It has many features which makes it different from other ECommerce Solutions. It is paid and you have to obtain a license to use it. Some of its features includes Recurring Billing, Payment Processing, Multiple Currencies, Tax Support, Quotes/Estimates & Ticket Billing,  Simple & Intuitive Interface, Fast Loading, Quick Setup & Friendly Design, Stock Mgt & Promotions, Many Payment Gateways, MaxMind Fraud Protection, Income Reporting & Statistical Reports,  Integrated ticket system, knowledgebase, downloads, announcements & network issues reporting, Create, Suspend, Terminate, Upgrade, SSL Certs, Update Nameservers, Client & Admin Area Templates, Order Forms, Language Files & CSS Styling, Module Development Kits, Action Hooks & Remote API.
5. CubeCart - It comes in two versions CubeCart v3 and CubeCart v4. It has also got a lot of features which are as follows Professionally Security Audited, 100% Template Driven, Customer Order History, Multi Currency Support, Tell a Friend. For More Details about this ECommerce Platform refer here.
6. PrestaShop – PrestaShop is a relatively new ECommerce Solution Compared to above ones but it is very competitive to all these. It has many unique features which provides this Solutions an Edge. It is free to use. Some of its features include Unlimited categories & subcategories, Full-featured WYSIWYG text editor, Unlimited product attribute combinations, SMS/Text-message alerts, Add/delete function modules,Bar codes, Bulk lister/import .CSV files, SSL (Secure Sockets Layer) encryption. Full list of features is provided here.

There are more ways to build these E-Commerce Sites, but these platforms are much popular than all others. Basically it depends upon the requirements or needs for which platform you can go by. In our view Magento is the Way-way ahead and much evolving ECommerce Solution and platform among all in the industry.