I’ve had a Navman 630 for some months now, and I’m very happy with it. The 630 is the predecessor to the 650. The big difference is the 630 uses an SD card to store the maps (limited to 256Mb by the hardware), whereas the 650 uses an internal 2Gb hard disk. The disk is large enough to have all the european maps pre-installed, although you can update things from your PC using USB as usual.
Things I like about the 630 are the large clear screen, the fact there’s an English voice available and the directions are clear. There’s a nifty ’3-D’ mode where the map can be adjusted from ‘flat’ to fully 3-D (i.e. using perspective) using the 8-way switch on the front panel. The big bonus for me is the fact that it’s a completely self contained unit and the only thing it needs is a power supply. I can move it from car to car very easily, which is a big bonus for those of us with multiple vehicles.
Update 27th Sep 2008: With the newer firmware and (larger) maps available since I wrote this original article, the maximum size of memory card has increased to 512Mb.