A new version (0150 BETA) of Processing got released today. It has many major changes to the previous (0148) and seems to have better support for vector and svg. Some libraries will have to be updated though. However - this gives me enough reason to list some of the libraries that drew my attention:

NextText (classes especially for text-based applications) uses TrueType fonts to render and display dynamic and interactive text.
(www.nexttext.net)
Geomerative (classes enabling extended 2D geometry operations)
also implements a TrueType font interpreter and importer to support the usage of typography in generative art.
(www.ricardmarxer.com/geomerative)
physics (classes enabling the simulation of physics) let you realize particle systems and forces more easily.
http://www.cs.princeton.edu/~traer/physics/
arcball (classes enabling easy 3D navigation) allows to freely rotate space along all three axes.
controlP5(classes enabling to implement controller easily) allows instant chance and feedback to different values for behavior parameters etc.
(www.sojamo.de/libraries/controlP5)