Cloanto, the company that owns the rights to the Commodore Amiga line, have a legal emulator that they sell called Amiga Forever. It's about half the price of one modern AAA game, and when you download it, it comes with about fifty games of varying notability, and there's many times more you can just install and play. And it's all legal.

I would love this to be the industry norm, imagine being able to download a NES! It's annoying that if we want future generations to be able to experience games of the past (whether to learn from them, or just for pleasure) we need to teach our children about piracy.