Steve's Carts 2 is the minecraft mod dedicated to let you experience the minecart system to its max. Instead of the three normal ones you can design your own. This is not a matter of making them looking as fancy as possible, even though many people would argue for them being fancy, but instead a way to add the features you would like to have in a cart. Features include but are in no way limited to drills, railers, solar panels, storages, wheat farmers, dynamite carriers, seats with steering ability, shields and shooters. Since the modules can be matched and mixed with very few limitations the number of carts that can be put together increases dramatically to an enormous amount.
Steve's Cart WikiEdit
You can find all of the info on Steve's Carts 2 [here]