html2xhtml converts HTML files into XHTML. It can fix many common
errors in HTML files (e.g. missing end tags, elements with incorrect
content model, non-standard elements or attributes, etc.) It can
also handle invalid or non well-formed XHTML input, and clean it
to produce a well-formed and valid XHTML output. The output document
type can be selected among several XHTML DTDs (1.0, 1.1, Basic, etc.)

WWW: http://www.it.uc3m.es/jaf/html2xhtml