W3C:
W3C XHTML 1.0 Standard
W3C XHTML 1.1 Recommendation
W3C XHTML Validation Service – will check an XHTML document for validity and well-formednessOther:
New! XHTML Book Reviews! – Find out which ones to buy and which ones to avoid!
WDG HTML Validator – a better validator than the W3C provides – more accurate
WhatIs.com an introduction to XHTML
Internet.com Webopedia a brief description of XHTML
Web Developer’s Library has some XHTML examples
Sean Palmer’s Extending XHTML articleNews Articles:
News.com article on XHTML
XHTML: Our Last Hope for Clean Code – webreview.com’s introduction to XHTML