We have modules for several shopping cart systems:
osCommerce 2.2 ms2 (http://www.oscommerce.com)
Zen Cart 1.3.0.1 (http://www.zen-cart.com)
Xcart 4.0.14 (http://www.x-cart.com)
Litecommerce 2.0.0 (http://www.litecommerce.com)
VP-ASP 6.01 (http://www.vpasp.com)
Mambo PHP Shop 1.2pl3 (http://www.mambo-phpshop.net)
Joomla 1.0.4 with Virtuemart 1.0.8 (http://www.virtuemart.com/)
Lightbox - for selling images online (http://www.lightboxphoto.com)
Drupal - (http://drupal.org/)

And have code included in several hosted shopping cart solutions:
Handy Shop  (http://www.handyshop.co.nz) (based in NZ)
Easy Store (http://www.easystorecreator.com)
WebfarmShop 2 (http://www.webfarm.co.nz)
Freeparking with SOHO Launch (http://www.freeparking.co.nz)
Mal's E-commerce (http://www.mals-e.com) (compatible with generic custom gateway facility)

Demo Shops (implemented using osCommerce)
http://nbnz.shop.paystation.co.nz