Bitchbot is a GPL'ed perl-based IRCbot that I coded mainly for #gloom on irc.edgeirc.net. The bot has a wide variety of useful and useless features, to name a few:
* factoids (bits of information about things)
* Game server query support for all popular FPS titles (using qstat, www.qstat.org)
* Message system for leaving short notes for people who are offline.
* Configurable access list to allow users to manipulate certain features.
* Channel operator commands (limited use; bitchbot wasn't designed to be a chanbot)
* Last seen nickname to find out when a user was last on the channel.
* Vote and poll on user defined topics.
* Channel statistics (if your server can handle the horrible memory leaks)
* Support for the cyborgizer and techifier toys from www.brunching.com.
* A ton of other stuff you'll find from looking at the command reference.