Natural products
Raw materials
Refined materials
Industrial manufactured goods
Consumer & commercial goods
Speciality goods
Research
Research is an odd category, because the most valuable developments are not often incarnated in material goods, and when they are, they're often one-off prototypes. This is a category where some additional engine support is probably warranted. Items here could well be generated somewhat on the fly as with something like http://www.cs.purdue.edu/homes/dec/essay.topic.generator.html or http://www-cse.ucsd.edu/users/mihir/crypto-topic-generator.html with appropriately defined lists that will generate items wanted by various specific user groups.
Contraband
See also