This is the one feature I miss most from MS Windows. Apple is getting closer with the latest OS X Lion. While there is still no keyboard shortcut (or memory that you like all your browser windows full size, if you do), you can now double click the "Go Full Screen" icon in the upper left corner of the window:
"Go full screen - Apps built to take advantage of the entire screen have a new full-screen button in the window title bar. Click it to expand the app window to fill the screen."
This alone is worth the $30 to upgrade IMHO!
You can also now drag from any edge or corner to re-size the screen.
Source, and more great features of OS X Lion:
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