Yesterday a new ecommerce module for Drupal, Ubercart, was announced. This is pretty exciting. I'd looked at the existing Drupal ecommerce module before, but it's a bit of a mess, cobbled together from what seemed to be endless disparate modules that half work together. (Not to belittle the achievements of the team which produced the ecommerce module: it has masses of functionality, and integration with all sorts of stuff; but it's too complex for normal people who just want to sell books or something.)
What marks out Ubercart?
The only issue I'm not clear on (probably somewhere in the documentation) is whether you could use it to build a electronic downloads site (e.g. to sell images or PDFs). I'm sure other stuff will crop up too (like currency handling).
This is a really exciting project, and is the kind of thing that could give Drupal a big boost as a general purpose web framework. It definitely looks like it could give osCommerce a kick up the arse. It's actually a joy to read the well-written, clear documentation (there are a few areas where it's incomplete, but generally it's pretty comprehensive). I've added it to my todo list of products to have a look at within the next month, and hopefully I'll end up using it myself (eventually).
Congratulations to the team, and I wish them the best of luck in getting it off the ground.