Devmap mode - useful for exploring a multi-player level that you don't know, but you want to find out what textures were used.

1. Create a new link to the multi-player EXE file [ "C:\Program Files\Call of Duty\CoDMP.exe" +set thereisacow 1337 +set developer 1 +set sv_cheats 1 +set monkeytoy 0 + set com_introplayed 1 ]
2. Fire up the link, type \devmap mp_hurtgen and then \cg_drawshader 1.
3. Point your gun at a texture.

Bubba's Arena Mapping - level design, prefabs

MODsOnline tutorials - more short tutorials

IWNation forums (adding gametype models) - How to add in search and destroy locations, etc.