I found that Ashop E-commerce was a perfect choice for some of my customers. It's simple to use and the support is pretty good. The only downside I found was that it can be slow sometimes (the admin section), that's about it. I wrote a review about them here: Ashop E-Commerce Review.
I seen quite a few people are favouring open source like ZS Cart I have heard that open source can be buggy, anyone knows one that isn’t?