Crutchfield.com offers the refurbished Kenwood 6.1" In-Dash GPS Navigation / DVD Entertainment System, model no. DNX5120, for $499.99
with free shipping
. It's $120 under the lowest total price we could find for a factory-sealed unit. Features include a 6.1" touchscreen LCD, built-in Garmin Navigation board with pre-loaded maps of the US, Canada, and Puerto Rico, DVD/CD player, compatibility with most iPod models, Bluetooth and USB connectivity, AM/FM tuner, and more.
Note that a 90-day warranty applies, although it's unclear who supports it.