Model Base - models/textures/scripts by the CA/zK team (?), mostly remakes of TA units
KaiserJ's "Lego" pieces - easily create units by puzzling together various "Lego pieces", comes with texture.
Widget-DB - you may use this for finding code samples
Various Resources by various people - cegs in .tdf format, bos scripts and some 404s ;)
Dario D.'s interface pack - contains textures and sounds, useable to make an interface