I believe the ALT key plus the mouse will allow you to grab any window and drag
it so you can see the top or bottom. ALT+F5 should unmaximize. This assumes that
you are using the default Gnome desktop. KDE uses different hotkeys for many
things.
Some useful links:
http://allhotkeys.com/ubuntu_hotkeys.html
www.ubuntu-unleashed.com/.../...ard-shortcuts.html