Xerces Java
Advanced XML parser, including support for XML Schema, DOM Level 2, and SAX version 2. [Open Source, BSD-like]

XP
Non-validating XML parser. [Open Source, BSD-like]

JDOM
Parses, manipulates, and outputs XML using standard Java constructs. API is similar to DOM, but easier to use. [Open Source, BSD-like]

IBM Alphaworks XML parser for Java
A validating XML parser for Java. [Freeware]

MinML
A small (~10Kb) Java XML parser. It accepts a subset of XML (it reads and ignores DTDs and does not support mixed content) [Open Source, BSD-like].

Resin XML
An XML parser which has SAX and DOM interfaces and XPath support. This is part of the open source Resin servlet engine.

Xineo OO Parser
A Java package offering an alternative to traditional methods for XML documents parsing. It allows large XML documents and streams to be parsed efficiently, while offering a convenient way to handle parsed data in an object-oriented way, allowing clean design and encouraging code-reuse. [Open source, LGPL]

Piccolo XML Parser for Java
Fast non-validating XML parser for Java supporting SAX 1, SAX 2.0.1, and JAXP 1.1. [Open Source, LGPL]

XML Pull Parser
A fast parser using a pull-based approach instead of SAX. It does not read DTDs and is optimized for small documents like SOAP. [Open Source, BSD-like]

kXML2
An XML pull parser and writer suitable for all Java platforms including the Java 2 Micro Edition (CLDC/MIDP/CDC). Because of its small footprint size, it is especially suited for Applets or Java appications running on mobile devices like Palm Pilots or MIDP enabled cell phones. [Open source, LGPL]

FastParser
High performance Java XML parser, can be used with embedded device. SAX, DOM Compliant. [Shareware]

JFIPA Parser
A set of Java-based tools that supports parsing and routing of envelopes/messages of the FIPA Agent Communication Language (ACL) encoded as XML. [Open source]

NanoXML
Simple and small SAX XML parser. Extremely small (6kb) version without SAX interface is also available. [Open Source, zlib/libpng-like]

Lark and Larval
Lark is a non-validating processor implemented in the Java language; it attempts to achieve good trade-offs among compactness, completeness, and performance. Larval is a validating processor built on the same code base as Lark.