Lobby Server

With TripleA 0.9 and greater, you can play in the TripleA lobby. Simply press the "Find Games on the Lobby Server" button on the TripleA start screen.

TripleA War Club

TripleWarClub is a PBEM ladder and is currently the best way to find opponents.

IRC

You can often find opponents to play online in TripleA's IRC chat room.

Server: irc.freenode.net

Channel: #TripleA

Or, if you are without an IRC client try the browser based client (requires Java.)