BigCommerce

I work for a wholesale business, and used BigCommerce for our company website. It doesn't give a lot of options for our business model out of the box, BUT I was able to customize it to fit our needs because you can modify the template files easily. Since then I've opened three more stores with them. One other thing worth noting is their support is great: the staff and other users will actually answer questions on the community forum, and when I have an urgent problem, Live Chat support is always great.
The downside to BigCommerce is their pricing plans are inflexible: For example, if you want 2GB of storage but not 1,000 products or tons of bandwidth, you can't just pay for more storage, but have to upgrade to the next plan. It doesn't appear as if they plan to change this either.
There are a lot of other issues (you can check the feature requests in the forum for more), BUT overall it's always been a pleasure dealing with this company, and they're always trying to improve their product. Definitely recommend.

They keep charging me for stores I have repeatedly asked to have canceled. They have also charged me for the same thing more than once a year (SSL certificates). Stay away.