What are your favorite resources?

So I haven't been around in while, in my absence, I scoured the internet for libraries that helped enhance my sites. What I want to know is if anyone has any libraries they prefer or have fallen in love with.

Heres my list of resources that I tend to use a lot:
jQuery (jquery.com)
html5shiv.js (@afarkas @jdalton @jon_neal @rem)
CSS3 Pie (css3pie.com)
background-size polyfill (github.com/louisremi)
Respond.js (j.mp/respondjs)
Skel (skel.io)

I definitely recommend Respond.js and CSS3 Pie they quite fancy ~~