Shoes - ruby in a box, with a simple to use UI library. Nice enough, but bundling its own version of ruby makes it awkward to integrate 3rd party libraries wanting a different minor version of Ruby. It has an excellent, and amusing, set of documentation.
The clojure language discussion of state discusses some of the problems of using an Actor and message passing approach to concurrency.
Jerome K. Jerome's idle thoughts can be read via Project Gutenberg.
An explanation of the FFT.
Games need artwork. Free artwork is a good thing. Good free game artwork is a very good thing. General program art is also good, especially for icons.
Applescript is evil. Langauge bindings for AppleScript are nifty. Enter appscript. Don't forget the tools needed to understand the AppleScript API being bound to, e.g. iTunes.
Ambulance driving and paramedic work - how to be under appreciated, overworked, and covered in bodily fluids all in one day's work - and in a free ebook, Blood, Sweat and Tea.
VirtualBox is a free VM, ala VMWare or VirtualPC. Also, free for 'personal' use, which does in fact permit commercial usage. User manual.
Flipcards, in python. Pyglet, OpenGL and sprites and animation and sound and stuff for games, in a nice package. Unlike pygame, easy to install. Pymunk, a pythonic wrapper around the chipmink 2D physics library. 1.1.3 needs a fix for crashes related to timers, caused by sound playing. Centering windows tip.
Google's protocol buffers make python data persistence easy, and should provide support for evolving data schema.