Linkshare has an "Individual Item Report" that shows which products were purchased.
Most major networks have the ability to pass a special parameter (SID at CJ, bfinfo at BeFree, u1 at Linkshare) that will get reported when there's a sale. You can use that to identify which keyword got clicked, which should give you some indication of which products are getting purchased. For instance:
Also, in CJ, sometimes the banners will have a "URL=" tag in them for the menu'd creatives, if you use this links independently for better targeting through PPC, make sure you add the "sid=" tag before the "URL=" otherwise it breaks the redirect to the consumer site.