I always choose something easy and fun every year. Last year I was Clark Kent - Superman shirt underneath a white button up, red tie, slacks, glasses. Done.
This year: Tony Stark. Black suit, White shirt, Bold Tie, a few LED's to make an Arc Reactor to put behind my shirt and I'm good. I'll probably shave my goatee in the right shape, too.
Maybe next year Men In Black or James Bond or something. Whatever's topical and easy.
2001 XJ Cherokee