Credits
Without the following individuals, groups and other sources, this project would not have been possible:
Project Coordinator: regurge
Authors:

regurge
new weblayout, keep the whole thing up to date

TheMuffinMan86
author of the original guide “The Ultimate Cvars and Commands List”, released back in the beta stage of Quake Live.

g0vn0r
added information to a hell of a lot of entries, many corrections, and generally helps to keep the guide up-to-date and correct.

Lorfa
cg_filter_angles, cg_levelTimerDirection default value fix,r_floatingPointFBOs reference, and many others…

Primary Sources:

id Software / QUAKE LIVE Forums
Quake III: Arena Source Code 3.21b – General console entries and descriptions.

“The Quake III Arena Bot”
Jean Paul “Mr Elusive” van Waveren – Bot / AI-related entries and descriptions

Holysh1t Quake Live Community / “Cvars and Commands List"
(Lashknife) - General console entries and descriptions

Vern Anderson’s Q3 guide
(full credits included on site) – Console entries from Quake 3 that are still present in Quake Live.

Other Contributers: Yakumo
Video Mode List corrections, added r_noFastRestart

Injx
Video Mode List aspect ratio fixes, wording/phrase corrections, flag legend improvement/correction

Bargle
added r_floatingPointsFBOs

Sm4rty
added r_aspectRatio
Notes

1. This list has been compiled over the years and includes Quake III Arena and Quake III Team Arena console variables and commands which have been included in Quake Live, some of which may or may not function or be applicable to the game. Use your own discretion.

2. Information has been sourced from many individuals and groups, and the applicable content that has been added has been paraphrased where necessary.

3. To report any errors in this guide, or help contribute, than you have the following options:

Recommended Links:
The QUAKE LIVE Console Guide - The Official Thread