D80 is a bit bigger, it has firmware updates/upgrades, more MP, bigger lcd, hi speed USB 2.0 (instead of full speed), uses SD cards instead of compact flash, obviously its newer.
But from what ive read and what not everyone says if your just an amateur just get a D70s, its cheaper and will allow you to get more lenses with the money you didn't spend on the D80.
I have a D70s and I like it, produces some good pictures.