There are some really amazing mods and mod packs for Minecraft out there, one of which is Tekkit, which is part of the Technic pack. It adds advanced electronics, alchemy, new ores and lots of various other neat things. Ever wanted to build a nuclear reactor in Minecraft? Well, now you can! There's tons of new stuff in the latest build that I haven't even touched yet, which blows me away since there was already so much.