CSE HTML Validator
Cse html validator is a powerful, easy to use offline html, xhtml, and css syntax checker/html validator, accessibility checker, and link checker for microsoft windows. a less powerful free version is also available.
http://www.htmlvalidator.com/
W3C Validation Service
W3c's easy-to-use
html validation service, based on an sgml parser.
http://validator.w3.org/