I use the Sony Handycam
TRV265E with the DV tapes rather than a card. You get loads more filiming time and it has nightvision, USB & Firewire download, 20x zoom, comes with good (if basic) sofeware and is around £150.
I use it on a suction mount looking through the windscreen or handheld (when I'm not driving
).
If you look at some of DVD cams then make sure they will download onto your PC, some will only download to a VHS or DVD recorder!!