Crap! It's trademarked by them too. I should've checked that first, sorry

There's also the "open" angle, which plays on the community and open source side of things...

Connected. Open. Commerce.

Something like "Connecting commerce" would be too close to the trademark, but the above would probably fly. Or...

Connected Community Commerce

I'd resist the urge to get too descriptive in the tagline -- the page title and other prominent marketing text is the place to introduce Drupal imho. As the UC founders have pointed out before, Ubercart has often brought people *to* Drupal in the first place. And honestly... "easy" is not really something I associate with Ubercart, when you compare it to the entire possible field of e-commerce options.

Like Ryan says, I like the ideas that could spin off of "Connect"...

Connect... to Drupal
Connect... to your customers
Connect... to community

I'm thinking from a visual perspective here