You can try to custom code your own e-commerce site by using Microsoft's "free" Commerce Server 2006. Of course, it isn't free, it's a beta version you can test and help debug for MS at the same time. As usual, you'll have to be approved before you can participate, but if you've ever considered working in the "big leagues," this is a great platform to get familiar with. Take a look at the technical overview and see if this sort of gigantic weapon is right for your arsenal.