For those who haven't heard-
Valve will release the source for Half Life 2(as they did for HL1).
Prima is publishing a book on coding mods for the game(or it explains the source code).
Anyways, there will also be a book published that shows what went on during the making of the game. You guys should check them out(Amazon "Raising the Bar")
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The RTB book comes out Thursday, and the coding one will be out December 14
Coding book
Raising the Bar