Foresight.js

Speaking of bandwidth media queries, this project by Adam D. Bradley looks promising:

Foresight.js gives webpages the ability to tell if the user's device is capable of viewing high-resolution images (such as the 3rd generation iPad) before the image is requested from the server. Additionally, it judges if the user's device currently has a fast enough network connection for high-resolution images. Depending on device display and network connectivity, foresight.js will request the appropriate image for the webpage.

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Foresight.js is a post from CSS-Tricks