get a treo 650 and then get either a bluetooth gps receiver or the gps cradle... tomtom works GREAT on it... great way to have one LESS device to maintain...

all of my cars have nav on it, including the beater... but my coworkers have the treo/tomtom combo and it really does work great... plus it has wacky voices you can switch at any time... weather and traffic is another nice touch.