I've spent some time over the past few weeks thinking about my favorite B2B ecommerce sites. Here are my current faves (in no particular order), and why.
Box's "Business" page is an easy-access portal to a complete set of product features & use cases. While I tend to recoil a bit at talk of "product features and use cases," the way they display them here is attractive and convenient.
Considering the breadth of Cat's product line, their main site is an exercise in simplicity. My primary complaint is their browse feature, which uses multi-layered dropdown menus.
Olympus NDT's video gallery gives one-stop access to hours of content - covering the lion's share of their product line. Considering that many of these devices run into (and past) the tens of thousands of dollars, being able to see them in action is a nice feature.
(I know they're primarily b2c, but whatever - *tons* of businesses buy tools on Amazon)
Amazon's "Improve Your Recommendations" helps users tailor the products that the site recommends them. For small businesses in particular, this feature can be really helpful in separating personal from business purchases.