The RedHat Interchange demo looks pretty good, a bit pricey tho.

Pricey? Try solutions from Software AG or, even better, e-commerce suite packaged with IBM WebSphere app server . How about 1/4M$ or so per processor?

Seriously, I suggest that you search for e-commerce or similar at Freshmeat. There are dozens of hits, but I don't know whether any will satisfy your needs.