The Martyr Java IRC Library - A library to manage the IRC protocol and client state in Java, separate from any client implementation. - http://martyr.sourceforge.net
Free Java Chat - Freeware Java chat applets to put on your website. Has ability to connect to IRC. - http://www.freejavachat.com
CBIRC - Powerful IRC client written in Java. Supports all common standards (RFC 1459/2812, ident, mIRC colors). A Java web start version is available. - http://www.bratschi.net/cbirc/
JWIRC - Java IRC client with unique features. - http://www.jwirc.com/
Apirc - ID Net - IRC Java Software. [Free for non-commercial] - http://www.prgs.id-net.fr/
Nitz - A Java based IRC Chat Client. [Freeware] - http://www.superior.net/~tech/nitz/
Alphaworks IRC client - From IBM research. [Freeware] - http://www.alphaworks.ibm.com/tech/irc
Relay IRC Project - Project aims to create an easy-to-use, multi-platform and scriptable Java-based IRC client and a set of Java classes for adding IRC capabilities to other Java programs. [Open Source, MPL] - http://relayirc.sourceforge.net
Lirc - Open Source Java IRC client that supports DCC and multiple server connections. - http://www.vonnieda.org/Lirc/