Not quite tutorials, but useful info that we had to share.

Build Errors See if your error is in here and if there's a solution to it.
CTF2 Map making guide Hal9000 guides you through the process of making a "good" and playable CTF2 map.
Quake 2 Entity list A list of all the entities in the game including the ones in CTF2.
Quake 2 Sounds All of those glorious sounds from the game described, organized so you know which is which and where to find them for use.
Colour chart An RGB value listing for you coloured lights, all the common and some not so common colours, and a sampe map for comparison of many.
Zoid's QE4 Guide The first QE4 editing guide straight from Zoid himself
Jailbreak A guide to help you make levels for the DM mod Jailbreak.
Wider is Better An excellent submitted (narrative) article on the wonders of using larger brushes and the effect on VIS.

Since we posted this it has generated more email then any of our other info pieces - if you haven't read it do so. It seems to work, tho the reason is debated extensively and the complete accuracy of some of the narrative statements within the article are downright disbelieved (for instance, Carmack has personally sworn never to IRC...).

Got another piece you would like to add? Let us know it.