http://www.magentocommerce.com/

It looks to be a very impressive open-source ecommerce system - much more feature rich than VirtueMart.

Trouble is, it doesn't look as though they have developed a component integration/bridge for Joomla yet.
Nevertheless, it looks very promising - if one could figure out a way to bridge user registration database.


Still, some of the future upgrades/features look very promising . . .

# Bundles
# Virtual products with support for downloadable products
# Support for grouped products built from configurable products
# Web Services API
# Gift Registry
# Gift Certificates (virtual)
# Customer Balances
# RMA support
# Drag n’ Drop design mode
# Banner Management
# Affiliates System (basic) and Campaign Management
# Backorders (full)
# Cost Management
# Warranties
# Subscription Management
# Required Items
# Recommended Items
# Strongly-Recommended Items
# Multiple wish lists
# Gift Wrap option
# Alternative checkout methods (multi-step, javascript free)
# Limited catalog access per user group
# Membership management
# Enterprise Search
# 3rd party integration ... (CMS, Payment, Shipping, Affiliate, Accounting, etc.)
# Improved import/export methods