Tools & Utilities
Editors
The defacto standard in level editing.
A Return to Castle Wolfenstein specific level editor.
Modeling
One of the most popular modeling programs out there. Very expensive, very thorough. It can do everything you need done and a lot you don't.
Probably the best (most popular) shareware 3D modeling program. Its only $20 US and does everything you need to create models. It is a great program to learn on.
The free version of 3DMax.
Miscellaneous
A must have. If you don't have it, get out from under your rock and get it. ;)