BuildCraft

If you are into technical Minecraft, or if you simply love building functional machines and systems, the BuildCraft mod will enhance your gameplay experience. The mod adds several new items that you can play around with to design efficient machines that will make your game much more cooler and easier. 

Take a look at the screenshots to see what you can expect from this mod. This is a Forge mod and download links are given below. Read the installation instructions carefully.