Internet Relay Chat (IRC) Help:Nearly 800 helpful files including FAQs, primers, technical guides, clients and scripts, and server lists and maps.
(Yet Another) IRC Information Website: Contains links, explanations, guides, and many good documentations.
Beginners Guide To IRC (mIRC style): Based on the chatting client, this is a good explanation on how to get started, easily. Contains plenty of other related links.
Client-To-Client Protocol (CTCP) Documentation: Specifications for CTCP as well as DCC protocols which are now standard supplements of IRC.
IRC Command Cosmos: Advanced reference of IRC commands.
Most updated RFC1459: IRC Protocol
Undernet FAQ Website: UnderNet's IRC-related FAQ
Undernet Routing Committee: Resources for Undernet server operators.