I'm happy to announce the availability of a new camera-control library for 3D sketches, PeasyCam ("P" for Processing, "Peasy" for easy-peasy).

  http://mrfeinberg.com/peasycam/

Development is hosted at google code:

  http://code.google.com/p/peasycam/

Sample:
Code:

PeasyCam camera;

void setup() {
    camera = new PeasyCam(this, 0, 0, 0, 50);
} 

That's it. Now a mouse left-drag will rotate the camera around the subject, a right drag will zoom in and out, and a middle-drag (command-left-drag on mac) will pan. A double-click restores the camera to its original position.

It is free for all uses, per the Apache 2.0 license. Please try it out, and let me know how it goes for you.