This page is intended to accumulate a variety of links to significant external SAX-related work, primarily using XML. There's so much SAX-related work that it can't possibly be a complete listing.
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SAX2 Parsers in Java
This is a collection of some of the XML parsers which support the SAX2 interfaces.
Also, since Sun's JAXP 1.1 API incorporates SAX2, any SAX parser bootstapped with JAXP 1.1 supports both SAX2 and the “SAX Extensions 1.0” interfaces. JAXP 1.1 is included with JDK 1.4, but you should manually update it to use SAX 2.0.1 instead of the older version (which is missing some bugfixes).
SAX1 parsers should still be usable with the SAX2 ParserAdapter class. (See the simple driver for XP, above.) Most of them have been updated to include SAX2 support. There's also the Docuverse HTML SDK which provides a SAX1 wrapper around the HTML parser found in Swing. (Swing's parser has significant limitations, but it may meet some of your requirements.)
If you're interested in SAX parsers that support only subsets of XML, there are a lot of them. For example, see MinML and MinML2. If the reason you're looking at XML subsets is parser size, perhaps for embedded environments, look at Ælfred2 to see about how small a fully conformant SAX2 parser can be. (That has a non-validating parser at its core, as well as optional validation and JAXP layers. It's larger than MinML2 since it supports all of XML 1.0 and XML Namespaces.)
Books and Articles about SAX2
There are a lot written about how to use SAX with XML. This is only a subset of the resources you can find.
Software Using SAX2
This is is an incomplete list of interesting software using SAX, which focusses on infrastructure rather than applications.
Of course, SAX1 applications still work with SAX2, although they won't be able to leverage XML Namespaces very easily, or work at all with information exposed through the extension interfaces.
SAX started out on the XML-DEV mailing list. That list is currently hosted at http://www.xml.org; you can subscribe at http://lists.xml.org/ob/adm.pl and view archives at http://lists.xml.org/archives/xml-dev (and there's also the old archive at Imperial College, URL TBS).
Current XML development uses the lists at SourceForge (see the Project Page link at the left), but issues raised on xml-dev will likely get appropriate attention also.