Here's a few thing I have tumble upon in magazine and everyday web life, which I think are useful to know.
Realistic drop shadows
This cool jQuery tool makes the generation and animation of box shadows very easy, just have a go, it's responsive to your mouse movements!
Clever date and timedelta management
Moment.js allow you to format dates and timedelta (aka date differences) very simply and quickly. I see it as a very good way to lift some backend processing and leave it the "bored" browser engine.
Masonry: The Art of filling empty space
You may have seen this on the increasingly famous Pinteresting.com
The tool allow you to place elements on a web page in clever floating way. While floating will float either to the left or the right, masonry float where there's space, either left or right. It's using absolute positioning with an algorithm that calculates coordinates, so it must be reinitiated when you resize your browser window.
Flotr2: HTML5 Charts