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
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).
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!!