This should be a complete list of all Quake 1 level editors, both old and new. I will try to provide links, screenshots, tutorials and help for each of them.
[last update: March 27th, 2013]
Kristian Duske | In Development | http://kristianduske.com/trenchbroom/
TrenchBroom is a cross-platform level editor for the Quake engine. It has a different slightly philosophy than other editors. I believe that the traditional approach, where you work primarily in 2D views, forces you to think in 2D rather than in 3D. That is why this editor does not have 2D views at all – you do all work in one single 3D view.
TTimo | 1.6.3 | http://icculus.org/gtkradiant/
The open source, cross platform level editor for idtech games
QuArK stands for Quake Army Knife and is a game editor for Quake and many other games. It can edit maps and models, import sounds and textures, create pak-files and run compilers.
Yahn Bernier, reckless | 0.96d | http://www.bspquakeeditor.com/
BSP is a freeware map editor for Quake, Quake2, Half-life 1, Hexen2, and other games based on these engines.
Baker | July 29, 2006 | 3.3 (with QuakeAdapter) | http://quakeone.com/qadapter/
Valve Hammer Editor
Download: Valve Hammer Editor (984)
[this page is a stub]
What details would you like to see here? Know other editors?