The search continues.... Leading the pack now:

ExpressionEngine - seems to be a fantastic CMS with a standard design-oriented approach to making page templates coupled with a lot of nice modules, including forums. Commercial at $285, but if it's as good as it sounds that's a small price. Huge drawback for commerce is that it has only a very simple store module that uses PayPal's cart feature. No on-site cart or killer item management. Speculation is that a full-blown commerce module will come with the new 2.0 version sometime this year.

Magento - looks like an excellent and clean upcoming full commerce solution. This includes templating like a CMS but geared toward a store-only site. This lacks the breadth of features found in EE above, but does the store and cart thing very well. Still in pre-release state with full production version scheduled for sometime this quarter.

If both of those were merged into one product I think we'd have the definitive winner here.

I find all this stuff super confusing. I feel like I had an easier time writing my shopping cart in PHP that wrapping my head around these systems. Probably because they throw around their own terminology and way of doing things. One great aspect to the above is that they both seem more flexible than many other systems out there in terms of page design for the front-end.

I could probably get away with converting my own site to EE and re-using my own PHP-based shopping cart. But my cart would not be a suitable solution for the other sites I'd like to get moved over to and developed with a CMS. Mainly because of larger item selection in their stores as well as needing the store owners to be able to make edits and changes themselves through a nice web UI.