It's OSCommerce for me to.
It has a massive community, who are also very helpful. There are many design templates available to give your shop the professional look. There also seems to be a contribution for most things that you can think of, making it very flexible.
Any body looking for a shop to be set up, please get in contact.
We are putting together a basic OSCommerce set up package to include a professionally made template from
www.web-sites.co.uk (Template Monster Affiliate Site) and set up of the software etc. We will be posting details on a separate thread soon.