ofxEdsdk allows for interfacing with Canon cameras from OpenFrameworks. This add-on enables people to control a Canon camera remotely, which is useful for project involving time lapses or photo capture at specific time frames. I myself have a high-quality Canon EOS camera at home; perhaps this add-on will allow me to put it to good use.
The ofxKinect is, of course, something that would come in handy for many new-media artists. There is a growing number of artists that use the Kinect for their projects because of its many applications and its ability to bridge the real-world with the virtual world. The possibilities of the Kinect are endless, so the ofx add-on for the Kinect is certainly a useful tool to have. (I’ve also stumbled upon some interesting reference material that teaches you how to use OpenFrameworks with the Kinect)
Box2D is a very handy physics engine that can simulate rigid bodies and was used in popular games such as Angry Birds. I had experience working with Box2D in Processing and found it to be a pretty powerful tool that facilitates the process of handling the physics of a virtual environment. Box2D is mostly useful when you have to simulate a large number of bodies that collide and interact with each other in some way (e.g. particles). It might be an interesting exercise to make a small project that uses this with the Kinect….