Last week I posted HTML5 Forms Styled With CSS3. There you can find useful links on how to style your forms and add effects with HTML5 and CSS3. I mentioned that beside for old browser fall back you won’t need Javascript.
But if you want to optimize your forms and add more options, Javascript is still needed. We are talking about less common options(not standard in every form) such as adding extra fields, password validator, file upload, etc.
A lot of jQuery plug-ins have become obsolete due to HTML5 and CSS3, those are mostly look enhancing plug-ins and text placeholder, which is now standard in HTML.
I have chosen the more common optimization scripts and almost all are simple ones making it easier to implement in your design or to customize. Forms are a very integral part of online interaction, it is the interface from which all data is submitted. An usable and easy to use form is guaranteed to be used again by your users.