Need database of categories for products and services
Classification is a really tricky thing -- a company that specializes in cell phones might have many categories of cell phones, while ones that don't might stop at a broader category.  Even within a given company, they might have multiple ways of looking at things, and so have multiple classification schemes / taxonomies / thesauri / ontologies / knowledge organization systems in use.

Just like any database, you have to know what sort of questions you're going to ask of your classification scheme, and from there, you can design what's going to fit it best.

A few registries / repositories / lists that I know about :


Taxonomy Warehouse
TaxoBank
JISC Directory of Metadata Vocabularies
TemaTres Vocabulary Server
Controlled Vocabulary Examples


You might also check to see if whatever organizations there are for your industry have any standard classification scheme / thesauri / ontologies / whatever.

Update : I don't know if the Global Product Classification might help or not.