Win + Pause/Break to bring up computer information and to access environment variables under the Advanced tab.
Win + R to go straight to the run box (though I barely use this anymore since I started with Launchy).
Of course Alt + Tab but also Alt + Shift + Tab for going backwards.
Oh, and personally, I hate Ctrl + F4 for closing tabs – too much of a pinky stretch.
Oh and try Win + Tab on Windows 7 (with Aero on).