Validators
Validate your web page
W3C CSS Validation Service - Validate your cascading style sheet (100 visits)
http://jigsaw.w3.org/css-validator/
W3C MarkUp Validation Service - A free service that checks documents like HTML and XHTML for conformance to W3C Recommendations and other standards (92 visits)
http://validator.w3.org/
XHTML Validation - XHTML and PHP in practice (98 visits)
http://www.deltascripts.com/phpclassifieds/xhtml.php