I'm really surprised no one has mentioned Big Commerce. I searched high and low for a ecommerce solution that has the robust feature set that Big Commerce provides and nothing comes close.
In the beginning of my search I was trying so darn hard to find something that integrates with Wordpress because I love it so much. But the top choices Shopp, WP Ecommerce and etc. did not have the robustness that I found in Big Commerce.
While Alan is right in that you need to follow the pre-design development process and figure out what fits your need, I took a really long view on my vision for my ecommerce website and wanted to pick a service that I could "grow" into. Big Commerce fits that need. Their platform has the balance of everything I was looking for.
