Commerce Server 2007
Commerce Server 2007 is a huge and powerful application but it is a problem to find documentation or material about it. Including the fact that there are not so many people working on Commerce Server 2007, it is a new product and there is no book, it should be a problem to start implementation.
Nikola Malovic has a couple of awesome posts on his blog site blog.vuscode.com about Commerce Server 2007. Follow the link and check them out.