Take the time to look at osCMax 2.1. The beta is being released in about a week. The current version 2.0.25 is loaded with features and 2.1 will be even better with one page checkout, updated SEO, overhauled BTS, jquery slideshow, super etc.
I have put on hold developing my cart so I can grab 2.1 and be set for a few years. Call me a fanboy, but from testing several open source carts osCMax blows them all out of the water. I went from installing about 14 mods using the sparse oscommerce version to installing only 2 mods using osCMax. The coding is a little bit different but not by much and it's a good different, IMO.