IRC

Free IRC Clients

• Bersirc - Small, lightweight and very nice! My personal favourite. Unfortunately Bersirc is DEAD DEAD DEAD. The client runs fine and its easy to use. But forget about docs (Site offline), source (site offline), or even its IRC channel (server offline)!
  
• Freenode Webchat - Join instantly without installing any software.
• IceChat - Open source, written in C#.
  
• HydraIRC - Website has been offline for several weeks, but supposedly very nice.
• Mibbit - Web based chat.
• Miranda
• VisualIRC - Scriptable and with a lot of nice customization features.

Non Free IRC Clients

• mIRC - One of the most popular IRC clients.
• Trillian