From IBM research. [Freeware]

ID Net - IRC Java Software. [Free for non-commercial]

Powerful IRC client written in Java. Supports all common standards (RFC 1459/2812, ident, mIRC colors). A Java web start version is available.

Freeware Java chat applets to put on your website. Has ability to connect to IRC.

jqIRC a java based IRC client. Source code is available.

Java IRC client with unique features.

Open Source Java IRC client that supports DCC and multiple server connections.

A Java based IRC Chat Client. [Freeware]

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]

A library to manage the IRC protocol and client state in Java, separate from any client implementation.