We live on Afternet (irc.afternet.org). We hang out in a channel #ludumdare. We announce the themes of current Ludum Dare events in the IRC channel FIRST. Outside events, the Ludum Dare IRC channel is a great place to chat with like minded game developers.
Afternet has a Web Chat Client. Embedded above for your convenience.
To learn more about Afternet, visit their website at afternet.org