Both are great cameras. D200 is meant for more advanced users who like to customize their settings. There is no preset program modes (like landscape, portrait, etc). It only has program, aperture priority, shutter priority and manual modes. It has more features than Canon 30D. It also has a weather-sealed body that the 30D lacks.
But the Canon 30D has a better high ISO performance with cleaner image than the D200, and to me this is more important since I take a lot of low light photos.
The D80 is good and is aimed at the consumer level customers, with preset modes and customizable modes. But it has a plastic body and not weather-sealed. And it only goes up to 3fps with continuous burst. High ISO performance is no better than D200. I won't consider the D80 as equivalent to the 30D or D200 in performance.
Well, enough is said of the specs comparison. The bottom line is that it doesn't matter which one you choose. The performance difference is not going to affect the photos as much as the difference in skills of the persons holding the camera. So stop worrying about which camera is the best, and focus more on improving the skills.
This is just like asking the question, whether Mercedes is better than Lexus. Which one has more safety features and better performance? These depend more on who drives the vehicle.