ComputerWorld published with it claims to be the greatest Windows tips of all time, you can read it over here. Here's a snip:
Toggle between apps: Use Alt-Tab to switch open programs without touching your mouse. The oldest--and still the best--Windows timesaver.
Navigate app windows: Press Ctrl-Tab to cycle through an application's windows (or through a Web browser's tabs). First cousin of the tip above, and probably the most underrated tip ever.
When in doubt, type it out: If you don't want to hunt through nested menus and the like, you can access most functions, applets, or files the old-fashioned way--by entering them into the Search box. Type Calculator, Control Panel, or even the name of a piece of music on your hard drive, and press Enter.