We use javascript validation almost everywhere we use forms. Validation is sometimes painful and we ned up repearing similar javascript code in several places. So I decided to search for some simple and easy to use libraries that can ease up the job of adding client side validation to my forms.
Continue reading about 10 Great Javascript Validation Libraries
A simple Javascript form validation library based on prototype.
Live Javascript Validation is a complete (radio & checkbox) client-side validation script .
Yav is a SIMPLE, POWERFUL and CUSTOMIZABLE javascript-based form validation tool. 
Validanguage is an inheritance-driven, open source javascript validation library designed to be the most feature-rich, user-friendly validation framework available.
JSValidate is a simple library based on Prototype and Script.aculo.us to allow you to do form validation.
You simply use special CSS classes to annotate your form and let the library do the rest.
LiveValidation is a small open source javascript library for making client-side validation quick, easy, and powerful.
Continue reading about LiveValidation – Javascript Validation Library
The TMT validator is a JavaScript library for form validation. It was developed with several goals in mind:
wForms is an open-source, unobtrusive javascript library that adds commonly needed behaviors to traditional web forms without the need for any programming skill.
Continue reading about wForms – A Javascript Extension to Web Forms
qForms JavaScript API is one of the easiest way to program HTML forms.