MLG (Major League Gaming)
http://www.MLGPro.com
Halo Pro (You can watch free Halo 2 Movies on this website)
http://www.Halo-Pro.com/movies.html
Bungie
http://www.Bungie.net
And hear is a forum based website for Halo 2
http://www.Halo2Forum.com

Hope that you find what you are looking for, and thanks for looking.