Stas Melnikov has compiled this list of JS and CSS plug-ins. There are numerous such lists, all useful, and worth looking at for inspiration.
http://stas-melnikov.ru/library-of-plugins/
[Github/loverjoel] is posting a new JavaScript tip everyday. Currently on tip #17 with previous tips all there to inspire.
Wondering how long he’ll keep going??
Definitely worth a look.
https://github.com/loverajoel/jstips