Application-specific integrated circuits, or ASICS, would be much more energy efficient for mining. As far as I know no one has done this yet. Field programmable gated arrays, or FPGAs, have been used. These also are highly efficient but can be prohibitively expensive... though cheaper than an ASIC.
There's one guy who has done asics, name of artforz. Also, have heard rumblings of someone that wanted technical expertise and wanted to spend some money. Search is your friend