Mac’s default Maximize button can be quite confusing for new users, especially for users migrating from Windows or Linux. Thankfully, Apple has now introduced a keyboard shortcut in Lion to Maximize a windows to occupy whole screen instead of just resizing it.
Here is how to get Maximize button to maximize to all the available screen space:
Click option+Maximize button (Green plus sign in upper left corner of a window)
In Mac OSx Tiger, Leopard and Snow Leopard
Download RightZoom for Mac from here: RightZoom.zip
Install RightZoom and open it. You can configure a hotkey to maximize key as well.