Are you wanting the mods to play singleplayer, or multiplayer? And How much of the game are you wanting to change?
If your looking for a total conversion and an easy to download modpack check out the Technic pack. It has alot of modern technical mods such as machines to build.
If your wanting some mods you can use on normal servers check out things like Rei's minimap, matmos, and sonic ethers shaders.