I'm currently using osCommerce for one of my sites and it has been good over the years, but I'm just finding myself at a stand still and looking to upgrade.
I've been researching other shopping carts and I've been looking into Magento. I like that it is also open source like osCommerce; so it gives me the ability to customize it to my needs through programming or using the community extensions. And also like that I can use M2E Pro extension to easily integrate with Amazon/eBay, but definitely need to tweak the code to get it working to my needs.
What shopping carts have you used in the past or currently using now? open source? saas? custom-built? Whay made you decide to use the shopping cart you are using now?