for last gen, I would say grab what is already worth a little bit on ebay, and chances are they may retain some form of value (Marvel VS. Capcom 2, Metal Gear solid 3 Subsisence LE) those are refering to PS2 games. I also tend to try and pick up the obscure RPGs that have been put out. NIS and Atlus rpgs tend to keep some form of value. Also if you were to keep certain games sealed such as those RPGs, you'll probably get a bit more for them.