I have no idea how implementable these would be, but can't hurt to suggest a couple of maybe-categories in the buy-sell menus.
Researchable: Items which can still be researched and produce results, whether they're one-offs or have getoneforfree still remaining. Probably best to ignore facility requirements or previously-required research.
Not researchable: The opposite of above - if you've gotten all you can out of researching this item, show it in this category.
Junk: Serving much like the Hidden category in the Buy menu, it might be useful to be able to flag specific items as vendor trash. Not quite sure how to work it from the UI perspective, since actually hiding items would case far more problems than it would solve. Possibly control-clicking an item changes its colour to purple to indicate it as flagged as junk?
