With the possibility to embed fonts in websites using @font-face CSS, some creative webdesigners developed their way to display icons using fonts, instead of images.
But most of the available icon fonts (or "font-face" kits) are paid, such as:
So, what free icons pack in font format do you know?
Please limit one "font-face" kit per answer - and include why you enjoy/recommend it.
This question can be converted into a community wiki, if the moderators want, because there is no best answer, and each response is welcome as a knowledge that can be enjoyed by many.