Most of my knives are in bad shape, so I'd been looking into a knife sharpener. I won't buy one—my knives aren't all that great in the first place and I'd rather find a local guy to just sharpen them anyway—but in my modest amount of researcher, it appears like the electric sharpeners from Chef's Choice, specifically the M130 Professional Knife-Sharpening Station Platinum, are about as good as it gets in powered sharpener.
The M130 is $150 and takes a little bit of practice (and manual reading) to get right, so it's probably best left to heavy cooks and the pros. If you'd like to consider a non-electric model, this thread by Chad Ward on eGullet will tell you just about everything you need to know.
Catalog Page [Amazon]