We love our GPS system—it's has saved our asses from having to go through the crack-whore district of SF more times than we can count. Our only complaint: not letting us change our destination while we're in motion. Solution? The Novogo V Series with voice activation. The voice activation lets you speak your destination (with your mouth), and the GPS will automatically change your way-point and calculate the shortest distance/fastest route.
The bad news, this Novogo V series is only available with UK and Europe maps for now, but hopefully that will change soon. There's also a Real Time Traffic Message Channel option for live traffic updates, and six different colors to match your car's interior. The unit starts at £279 ($513).