D80 uses SD, D200 uses CF. D200 is weatherproofed, D80 isn't. If I had been able to afford it, I would have gone for the D200 instead of my D80 but at the time it was about another 50% extra. If you have the money, I would suggest that you pay the extra and go for the D200; I'm always reluctant to take my D80 out in light rain but if I had got the D200 I would not be bothered so much.
Edit: Also in the fullness of time when you come to upgrade again, I am sure that the D200 will be worth more (but not necessarily that much more)
-------------------- Too many cameras, too many lenses.......