I've been playing with the Koala XSL Engine today. It uses the Docuverse DOM SDK (formerly known as FreeDOM) and seems to work straight out of the jar. From the documentation the package supports...

     </p><blockquote class="iquote">"...matching patterns, every templates rules such as numbering,literal result elements, literal text, processing and direct processing (xsl:for-each, xsl:value-of, ...), using string expressions, attribute value templates, string<br class="nl" />constants, including stylesheets..."</blockquote>...but does not yet support...<p />
     
     <blockquote class="iquote">"...Flow Objects, macros, imported stylesheets, templates matching on id, priority, matching on positions, white spaces in patterns, conditional processing, named attribute sets."</blockquote>I'm planning on using it at work as an enhancement to an HTML publishing system I wrote last year and eventually (when I get time!) I'll be using XSL to transform this site automatically.