Javascript pros will probably know about this already but for those of us only occasionally diving into the javascript world this might save some time when looking for small libraries for specific purposes.
When jQuery and all the others are just too much or indeed too heavy for your has-to-be-ultra-lightweight project but you need CSS selectors or templating or simple animations or stuff like this you want to check out microjs.com.
For a small mobile HTML5 app I am experimenting with I needed CSS selectors, traversing and manipulation and a bit of templating.
As I am used to jQuery the obvious choice was Zepto.js which feels just like jQuery but is much smaller (with much less functionality of course). Now for the templating I went to use ICanHaz.js which is mustache compatible and works like a charm.
Make sure to bookmark that site. microjs.com