dom4j
dom4j is an easy to use, open source library for working with XML, XPath and XSLT on the Java platform using the Java Collections Framework and with full support for DOM, SAX and JAXP.

JDOM
JDOM is a Java representation of an XML document. JDOM provides a way to represent that document for easy and efficient reading, manipulation, and writing.

JiBX
JiBX is a framework for binding XML data to Java objects. It lets you work with data from XML documents using your own class structures. The JiBX framework handles all the details of converting your data to and from XML based on your instructions.

NanoXML
NanoXML is a small XML parser for Java. NanoXML comes in three different components: NanoXML/Java (The standard parser for Java); NanoXML/SAX (A SAX adapter for NanoXML/Java); NanoXML/Lite (An extremely small (6KB) XML parser which is the successor of NanoXML 1. It only provides a limited functionality: no mixed content and the DTD is ignored).

NekoPull
NekoPull is an XML document parsing API that extends the Xerces Native Interface (XNI) to provide pull parsing functionality.

Phoenix
Phoenix is an information extraction engine developed by the University of Würzburg, Dept. It extracts structured information (e.g. addresses, medical cases, ontologies) from any kind of XML document (e.g. unstructured HTML documents or OpenOffice text documents).

Piccolo
Piccolo is a small, extremely fast XML parser for Java. It implements the SAX 1, SAX 2.0.1, and JAXP 1.1 (SAX parsing only) interfaces as a non-validating parser and attempts to detect all XML well-formedness errors.

Xerces Java Parser
The Xerces Java Parser 1.4.4 supports the XML 1.0 recommendation and contains advanced parser functionality, such as support for the W3C's XML Schema recommendation version 1.0, DOM Level 2 version 1.0, and SAX Version 2, in addition to supporting the industry-standard DOM Level 1 and SAX version 1 APIs.

XMLBeans
XMLBeans is a tool that allows you to access the full power of XML in a Java friendly way. It is an XML-Java binding tool. The idea is that you can take advantage the richness and features of XML and XML Schema and have these features mapped as naturally as possible to the equivalent Java language and typing constructs.

XOM
XOM™ is a new XML object model. It is an open source (LGPL), tree-based API for processing XML with Java that strives for correctness, simplicity, and performance.