This is a slim jQuery form validation Plugin. The core is under 6kb and can be extended with your own validation functions. Also you have full control over the behavior and style of the error-containers. It comes pre-styled and with 16 pre-written validation functions. Demo Source

With this Plugin you can style your markup right in your browser with a build-in element selector and CSS editor. Generate the CSS code of altered elements with one click and use it in your own stylesheet. Demo Source