Recs.
Updated
SpecsUpdate
Pros
Pro Great interface
XChat's default interface is clear, well-organized and intuitive. Channels can be laid out as both tabs and in a tree structure. All components such as user lists, topics bar or even menu bar can be hidden to provide a clean way to interact. Conversely the interface can be configured to show quick access buttons for changing channel flags, sending files or performing operator actions.
Pro Functionality can be expanded with multiple scripting languages
XChat supports scripting in Perl, Python, Tcl, Ruby, C++ and ECMAScript Scheme (Guile). All languages can be used to extend functionality of the software - bots can be written, automation can be added, new dialogs can be created.
Pro Functionality can be extended with plugins and scripts
XChat has a great list of plugins and scripts. Most quality IRC clients support plugins but XChats library is incredibly extensive. They include functionality ranging from randomizing away reasons to building a full-blown file server. It's possible to add an RSS feed or play a game of chess. Or maybe you want to control an mp3 player via chat while translating everything you type to l33t speek. XChats Plugin Library is truly extensive.