HTMLtidy validator (Firefox extensie)
HTMLtidy validator (Firefox extensie)
http://users.skynet.be/mgueury/mozilla/
W3C HTML validator
W3c's easy-to-use
html validation service, based on an sgml parser.
http://validator.w3.org/
WDG HTML validator
The wdg validator will check the syntactical correctness of your html to help you produce more accessible web pages.
http://www.htmlhelp.com/tools/validator/
Webstandards checklist (Maxdesign)
A site built to web standards should adhere to standards (html, xhtml, xml, css, xslt, dom, mathml, svg etc) and pursue best practices (valid code, accessible code, semantically correct code, user-friendly urls etc).
http://www.maxdesign.com.au/presentation/checklist.htm