^IO^L!nks 

Openarena general
Openarena forum
Openarena Serverlist | + players
OpenArena Wiki
Random screens
GTK radiant (create maps)
Topic about setting up GKT radiant
Mapping tutorial

Openarena communities, tournaments and stuff
Official openarena community forums
Openarena Argentinia
Italian community
Czech community
French community
German community forum
OpenArena Clan League (tournament from march 2010 - end 2010)
OAchallenge (tournament from end 2009 - begin 2010)
*r's list of clans, complete with websitelinks and players ^^

Openarena clans
AFO
[CZ]clan
Elite Clan
Evil|Clan
GaNja clan
GoD|Clan
/NIN/Clan
/oaN/clan
Revolution clan
RN|Clan
=SC=
supeR,Bots

IRC channels
OpenArena: #openarena@irc.freenode.net
IO-clan: #ioclan@irc.quakenet.org
*revolution clan: #oa-revolution@irc.quakenet.org
NIN-clan: nin-clan@irc.quakenet.org
QTF-clan: qtf-masters@irc.quakenet.org
Evil-clan: #evilclan@irc.quakenet.org
Pi.Clan: #endlessoa@irc.quakenet.org
AfterShock (oaUnofficial): #oaUnofficial@irc.quakenet.org
AFO-clan: #les_afo@irc.freenode.net
GOD-clan: #god_oa@irc.freenode.net

Mods
Excessive Plus (E+)
OATMEAL mod everything you want yourself
OA-RPG
TeamFortress Mod
Powerball mod
CPMA (aka promode)
OANAGE mod
Q3Rally

Utilities
OAcon

Other links
400kg Aim Training