Mac OS X Shortcut Maximize window

Is there really no way that I can maximize or unmaximize a window in Mac OS X with just the keyboard? (Currently using 10.6.3)

Have a look at RightZoom which is a freeware application for exactly that purpose: It provides the possibility to define a keyboard shortcut for maximizing windows and can override application specific behavior for the green resize button to make it consistent for all apps.

Most Applications have "Zoom" or "Zoom window" commands under a "Window" menu or equivalent. I think the most straightforward solution is to type the following in the terminal:

defaults write NSGlobalDomain NSUserKeyEquivalents '{"Zoom" = "@^Z"; "Zoom Window" = "@^Z"; }'

That command will set the default keyboard shortcut to ⌘+control+z

I use SizeUp. Lots of functions via Keyboard.