Have more than 1 drop down in inventory depending on the tiers you have in Category editor. We have Type of appliance>Brand>Type of component.ie:Maytag>Dishwasher>Electrical parts.
So it would split the category selector in Add new inventory item to three drop downs. 1 for Type 1 for Brand and 1 for Component type. We have a list of over 100 to scroll through when we add a inventory item.