A Youtube channel made to compile as many Halo Custom Edition video tutorials as possible. Here are some sites that can help you learn about Halo modding and mapping:
http://www.halomaps.org/
http://ghost.halomaps.org/tutorials/
http://www.modacity.net/forums/index.php
http://www.halomods.com
http://www.modhalo.net/
http://halo2.filefront.com/
http://forums.filefront.com/halo-series-861/
http://gbxforums.gearboxsoftware.com/forumdisplay.php?f=10
http://www.bungie.net/Forums/topics.aspx?forumID=2
For extra tutorials that won't be found on this channel, be sure to check out Yoda's channel here:
http://www.youtube.com/user/Yoda73811