My friend Steve (blog) sent me an email about a pretty cool car GPS navigation device. The TomTom Go, is a portable in car navigation device that incorporates navigation software, maps and GPS receiver in one device. It has voice prompts, 3D maps, and a touch screen.
It looks like it is not CD or DVD based, so I assume that there is a USB connector or it takes some flash media to load the maps. The map for the state of California is about 66Mb, according to their web site, and they do offer regional maps.
A car kit is available which offers Power supply, audio out, audio mute, audio in, and disconnect signals, so it seems like it could be integrated pretty well with a pre-existing head unit.
The one downside for this product, is that it doesn't appear to be a double din mounting kit. I would love it if this could be integrated into the dash, as opposed to sitting on top of the dash