Trying to find a good replacement was hard until we found MijoShop, which we quickly found to be the best match for the site.
We needed some new features, so I contacted Denis (from MijoSoft) and he quickly pointed out how to do those by myself. I decided to give them back to the project and all my changes got quickly included to the distribution. They also implemented a few other small but important improvements based on our discussions.
I cannot be more happy: this is the first shop solution that really works for us and the support has been nothing else than perfect for me.
They even gave me a free subscription in return. :)