I have only used a handful, but the one I liked the most was Magento. Although it was difficult to learn how to theme, once I understood how everything worked it got easier and easier. Mainly because it has two parts, the template (layout and structure) and the skin (styles and appearence) so you can change only one of those parts and make a huge difference in the design. It is also tiered so that if you only want a new skin to change one CSS file, everything not included in that skin will default to the default skin for your site.
Thanks for the suggestions, I’ve heard a lot about Magento, people seem very split down the middle with it. I hear it’s very resource intensive and bloated from some, others say it’s comprehensive and amazing. I will definitely look into it.
Since I use WordPress religiously, I would love to keep things integrated, I guess I have just had bad experiences with them so far. WP-Ecommerce left a bad taste in my mouth unfortunately.
Either way this weekend looks like it’s going to be full of testing and learning… beautiful. :)