Depends on what you mean by never get bored. If you mean what I can pick up and play and still enjoy, then I have a host of games. Ranging from Ocarina of Time, Castlevania Symphony of the Night, Muramasa: The Demon Blade, Metroid II, Smash Bros Brawl, Capcom vs SNK 2, Chrono Trigger, Dragon Quest VIII, Sim City 3000, etc.
However, as for games I play consistently that I never get bored of, I don't really have one of those. I can't just play a game non-stop forever.