I went for a complete no brand Chinese model with a 7" touchscreen, bluetooth for hands free connection to your phone, Sirf IV atlas chipset, 500mhz processor, 2gb built-in memory and SD slot which takes up to 32gb cards, headphone socket, video in so you can use it as a monitor, RF out so you can tune your radio into it for better sound, video playback, MP3 playback, picture browsing, built-in games. It runs on Windows CE 5.0, so there are plenty of apps for it.
It came with IGO 8.3 software and europe maps on the internal memory, but on the Sd card I have IGO 8.3 with US maps, IGO Primo with Europe maps with 3d maps & buldings and TTS voice, Ndrive with Euorpe maps, Automapa with Europe maps, TomTom with Europe & US maps, Sygic with Europe maps, all running of a menu system, with around 20 different apps and games.
I've used it loads of time and it's never had any problems, apart from the fact that a 7" screen is a bit big on the dash so I have it in front of the radio.
It cost me £65 with free delivery. I didn't buy from ebay as they are selling for over £100, I got it from pandawill.