There's a collection of shortcuts that do various actions in Windows. These are ones I've known and used. A full collection can be found at http://support.microsoft.com/kb/126449.
Windows Key => Open the start menu
Windows Key + D => Minimize all windows and show the desktop (or restore it)
Windows Key + E => Open a new Windows Explorer window
Windows Key + F => Open a new Search window
Windows Key + L => Lock the computer
Windows Key + M => Minimize all
Windows Key + R => Open a run prompt
Windows Key + Pause/Break => Open the System properties window
Windows Key + Tab => Cycle through the applications along the task bar
Windows Key + Ctrl + Tab => Cycle through the quick start, desktop, and system tray.