1. Sid Meirs' Civilization (The Original)
Played the shit out of that game as a kid/teen
2. Ultima IV: Quest of the Avatar
Played that game for as long as my NES held off. That was real UO, where you actually had to read the moongate to travel through them and what not. Only pleasant memories from this game, I think I'll start it over again!
Romance of the Three Kingdom II (SNES)
I still do, and will always play this game when I don't know what to do. I've beaten it countless times, I know every details of every generals that is important to know, and yet, I just never get tired of it.