Ketchup is a slim jQuery Plugin that validates your forms. It aims to be very flexible and extendable for its appearance and functionality. Although Ketchup is designed to be styled and extended by you, it already looks tasty and gives you the most common validations by default. If there is no validation fits your needs, you can always write your own too. You can make your own ketchup with ease.

Requirements: jQuery Framework
Demo: http://demos.usejquery.com/ketchup-plugin/
License: MIT, GPL License