Bluetooth: Many midrange and virtually all premium navigation devices include a Bluetooth speakerphone interface. Garmin's works well with most phones and does autoreconnecting as well as reading contacts from your phone. And the Bluetooth interface on TomTom's new GO 2000 series works well with the Motorola Droid X phone. Magellan, though, is still playing catch-up in Bluetooth capabilities.
Text-to-speech: Virtually all devices except for the least expensive entry-level models now include this feature. (Text-to-speech reads directions aloud to you.)
Unique features: All the manufacturers try to add something unique to set their devices apart. Magellan, for example, offers a One Touch interface for single-tap access to favorites or stored searches. Some devices supply the AAA TourBook as well as a points-of-interest database. TomTom's IQRoutes is a routing feature that uses historical traffic data plus community-based map updates. And Garmin's newest Nuvi 3790 models have an ultraslim case with a multitouch, high-resolution 800-by-480-pixel glass screen that provides 3D building and terrain views.