What is a good pre built estore - cart, inventory, shipping tracking, invoicing, etc

I've got an in-house estore that has become hard to maintain and I'm considering replacing it with an existing robust system. I'm looking for something with:

front end - browse & buy products, the look must be completely customizable
back end - edit products, product options & prices, product categories, etc
inventory - number in stock, low inventory warning, limited qty (no back order), min qty orders
billing - bill to credit card or account, calulates total including taxes & shipping
invoicing - partial shipments & payments, record of transactions, ability to make reports directly from db
bilingual - French/English front end at least

I'm more familiar with Microsoft .net/asp, MSSql Server, COM, XML/XSL - but I'm open to any products that you've found robust and easy to work with.  I will be host several estores on different URLs, same web server though.

Thanks.