If you'd rather shoot Nazis on the go, then Wolfenstein 3D Classic Platinum for iOS will be free to download later today, for a limited time only. You can also listen to John Carmack reminisce about the game's development in a special Bethesda Podcast post.
I have good memories of Wolfenstein 3D. For a long while, my grandfather had a better computer than anybody, and he had a load of games for us. Commander Keen, Duke Nukem, Gods, and Wolfenstein 3D ate up many hours. Good times, good series. Even that last sequel, which was surprisingly fun!
Anyway, happy birthday, Wolfenstein.