This is a hard one to answer. But here is a list.
Favorite game of all time would have to be Smash Bros. Melee. I believe that it is the greatest Multiplayer and 1on1 contest ever made. It also has a great single player and adventure mode. I never get sick of this game and will play as long as I have a willing opponent.
Any Zelda Game (Espeically Wind Waker and Zelda3)
Any Metroid Game (Espicially Prime and Echoes)
Final Fantasy V (The others too, but especially 5. I played it through 3+ Times)
Most of the 2D Mario Games (The 3D ones were ok, but just didn't do it for me)
Smash Bros. Melee It is by far my favorite Modern Multiplayer game.
Super Mario Kart (SNES). I still love this game and am lucky to have 2 friends that love it too! None of the newer Mario Karts have as good of a Battle Mode.
As far as PC Games, I spend plenty of time playing Doom2 (Zdaemon) and Worms2 as well as Zelda Classic.