This isn't just some long collection of links. This is a list that I continue to use, to learn new stuff and remember old stuff.

MAPPING FORUMS - never leave home without reading them.

TramDesign: wolf mapping forum full of great minds. wolf mapping section of the larger forum group. Full of great British minds.
Splash Damage: wolf/ET mapping forum and more importantly, home to the q3map2 support forum. Get your answers directly from the man himself.
Planet Wolfenstein: wolf mapping forum full of many minds. Doom3 mapping forum where some of the most informed minds on the subject meet.

MAPPING TUTORIALS - never grab the mouse without them.

Surface Tutorials : excellent tutorials on many mapping topics featuring how to create objectives.
TramDesign Resources : a great collection of tutorials featuring creating ROQ files, levelshots, mortars, and many more.
Nib's Resource Center : some good beginner tutorials as well as very good tutorials on lightmapped terrain and sky portals.
Kos' Virtual World : tuts on lots of SP wolf issues, as well as MP. Lots of cool script mover and effects tutorials as well as rain and lightning.
FPS Tutorials : great tutorials on topics like getting rid of sparklies, lighting, and manipulating patch meshes. You must enroll in Patch-Mesh 101!
Lightfilters : a really cool tutorial on using 'surfaceparm lightfilter' for stained glass type effects. Unfortunately in German. Worth the effort translating though.
Performance Testing : a manual of sorts that has an excellent section on Performance testing and packaging your map. Not strickly for wolf, but valuable info regardless.
Skewing and Bending : an interesting tutorial on complex brush arrangements.
Rubble and Ruins : a very handy tutorial on creating good debris.
Alpha Channel Textures : a nice beginners look at creating your own alpha channel textures.

TEXTURES AND 2D ART - never touch your wacom without them. : huge collection of Photoshop tutorials from creating textures and patterns to creating web interfaces.
Pinoy7 Tutorials : good PSP tutorials on metal, pipes, etc.
Qbranch Tutorials : excellent tutorials on creating textures and shaders for models.
6thfloor Tutorials : good tutorials on tiling textures and creating reflective glass shaders.
Tutorial Warehouse : nice collection of texture tutorials and techniques.
Eyes on Design : top notch tutorials on creating great web art. Some techniques can also be applied to creating game textures.
Grunge Map Tutorial

CODE MOD TUTORIALS - never open your editor without them.

Index of mod Tutorials
Info on messing with menu files