I highly recommend OXO Good Grips Pro Y-Peeler. It really provides something to hold onto, preventing many sliced knuckles and fingernails. Notice that OXO makes a less expensive version, but the frame is entirely made of plastic. =/ Stick to the metal frame.

As for other garnish tools... Most everything else stays in my kit bag nowadays. A good knife is really the only addition I'd suggest. If you really want to get into fanciness, a decent melon ball scoop/cutter set can be helpful sometimes. However, I generally prefer my cocktails sans balls.