This thread exist as a overview of what useful threads there is. So that some doesn't get lost which aren't stickied, and that there won't be so many stickies in the first place.
If there is anything you want to learn you should check this thread first. As times goes on, more stuff will be added here to the first post, so you won't have to scroll or search through pages (if they happen to come).
Tools/Applications:
Blender - 3D application: Click me
NetRadiant - Mapping/Level Design application (designed for Nexuiz): Click me
MaPZone - Create your own procedural textures: Click me
Models/Player models:
How to Create Player Models: Click me
How to Create Models: Click me
Mapping/Level Design:
Shader Manual: Click me
Shaders - Explanation: Click me
Level Design Training Videos: Click me
Hint brushes - Explanation: Click me
Onslaught Tutorial: Click me
Map .pk3 Layout and Information About .mapinfo: Click me
Tutorials:
Blender Video Tutorials - With focus on games (Very good): Click me
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PS. Any admins and moderators with power can feel free to add and change stuff in this post as well.