javascriptvalidationformslibrarymootoolswebdevelopmentfValidator - An open source (free) unobtrusive javascript tool for easy handling form validation
fValidator - An open source (free) unobtrusive javascript tool for easy handling form validation zend.lojcomm.com.br
"An open source (free) unobtrusive javascript tool for easy handling form validation." Looks ok, but shame it's Mootools and not jQuery (making it useless for us).