Creating a shortcut for Zooming (maximizing) windows that actually works on every app?
The following Applescript will trigger the zoom button (that´s button 2) in the frontmost application´s window.
You could make this a service and define a global shortcut for it or use an application like quicksilver to call it.

tell application "System Events"
set frontApplication to (get name of every process whose frontmost is true) as string
tell process frontApplication
    click button 2 of window 1
end tell
end tell