Option + Tab, Option + `, and Exposé do a good job of that for me. Plus if I don't maximize my windows that is a form of wasting space.Why? Talk about wasting space. If you maximise all your windows you can only see one application at a time. When I have my windows setup properly I can be using 3 or 4 different applications and never have to move or resize windows to expose what is in the other programs.
That is my number hate on Windows, the fact that windows are pretty much always maximised and making sure they are not maximised wastes even more space because each window has it's own separate menu bar unlike Mac OS X which only has one menu bar which reflects the currently active application.