In somewhat alphabetical order:
All Seeing Eye Server Browser
http://gamesdomain.yahoo.com/ase/register
Clan 4u2
http://www.clan4u2.com/
Clan BTF
http://www.clanbtf.net/
Clan Devine
http://devine.murder187inc.com/
Clan DWx
http://www.dogsofwarclan.net
Clan KEA
http://www.clankea.com/
Clan KIL
http://www.clankil.com/
Clan LOF
http://www.lethaloldfarts.net/intro.asp
Clan MOD
http://www.fulltimewebmaster.com/myforum/mastersofdeath.html
http://www.freewebs.com/modclanq2/
Clan SIR
http://www.freewebs.com/sirclanrox/home.html
Clan SX
http://souljasx.tripod.com/
Clan TNP
http://www.angelfire.com/ri/tnp/
Clan Virtue
http://www.thegeekcentral.net/virtue/
Clutch Gaming
http://www.clutch-gaming.org/
CSports.net Ranking system
http://www.csports.net/
Dukie's Front
http://dukieskinz.homestead.com/dukiesfront.html
Echon EGL client
http://www.echon.org/
EnterTheGame
http://www.enterthegame.com/
HolyWater AntiCheat client
http://www.q2players.org/holywater_v.16a.zip
Map Downloads
http://www.clanwos.org/maplist.htm
NoCheat AntiCheat client
http://bryceinc.com/
NoName Script for irc
http://www.nnscript.de/
Pan's Page for Map/Map Making
http://www.home.versatel.nl/djbloot/
Planet Quake
http://www.planetquake.com
PolyCount
http://www.planetquake.com/polycount/
Q2Advance AntiCheat client
http://www.q2players.org/q2advance/q2a1.0b5.zip
Q2Cafe - Map Making
http://leray.proboards34.com/
Q2players.org
http://www.q2players.org
XFIRE
www.xfire.com