Robert Hall wants a keyboard shortcut for maximizing a window.
There’s no way to do this with one keystroke. But you can do it with two.
If you want to maximize an application window, press ALT-SPACE. (In other words, hold down the Alt key while you press the space bar.) This will pop up the current application’s System menu–the same one you get if you click the little icon in the window’s top-left corner. Once the menu is up, pressing x will maximize the window. You can also press n to minimize it or, if it’s already maximized, r to restore it to its pre-maximized state.
What about a document window within an application? Assuming the application supports the Multiple Document Interface (MDI), press ALT-HYPHEN (in other words, hold down the Alt key while you press the hyphen or – key) for the menu. Then follow the same instructions as above.