Here is a set of 4 icons for OS X Leopard which are perfectly suited for the GTD ethos. They each come in 4 different sizes (512,128,32 and 16) and come in a variety of filetypes (PNG, ICNS and PICT Resource file).
These icons can be used on personal and work computers, but cannot be sold unless heavily modified.
Please let me know how I can improve these, different symbols etc. ^_^