Try to keep an open mind for open-source software. Its community supported and community designed and doesn't come with any proprietary stuff attached to it.
I feel somehow nostalgic, i had this question once when i started to investigate Shopcarts to use and everyone mentioned a different one, most of them the ones here and in the end i ended up with Virtuemart. You can try most of them since theyre free but i made an instalation of Joomla added Virtuemart to it and a nice template from rockettheme (they have developed a really cool one to be used with virtuemart) and as far as i can tell you it's one of the best open source shopcarts out there. Theres also a tool specifially designed for it to upload .csv files in case youre interested called C.S.V. Improved 1.5 very flexible and costumizable. Good luck with your Store.
osCommerce is pretty much industry standard (in north america at least) and has been for free. Good & cheap (free) way to get an online store store up and running with lots of plug-ins. When you need more power, graduate to their paid version called CRE-Loaded. Magento is another good one, I'd probably say #2.
3 weeks ago i was in the same position. well it depends what do you want. i think prestashop and magento. Both are free. magento is pro but i don't reccomand it unless you want to make some big fancy shop. prestashop is ok. source code is very clean and you can add very easy new modules. i also find some nice free templates. I'll choose prestashop