Parsley
Validate your forms, frontend, without writing a line of javascript
... will follow! Parsley is shipped with more than a dozen useful validators. If not enough, use the awesome Parsley extra Ajax validator or tons of other extended validators provided by the community. Parsley strongly focuses on #UI and #UX. Override almost every Parsley default behavior to fit your exact needs. Still ships almost bug free. Parsley is strongly tested, and aims to work on every browser (including IE8).