Aww, you guys are so boring! :3
With Minecraft, mods are becoming something you need rather than something you want. Almost every MC player has mods, the game is so much better with them in. Tekkit and Feed the Beast are the most common, but they're a collection of mods rather than just one, but it gives you so much more to do and it's a lot more interesting with a few thousand more items.
Minecraft and Garry's Mod are really the only things I bother using mods for, they're just the sort of games that require them. I haven't used mods in any other game, normally I would see it as pointless and a waste of time.