You may sometimes come across a window which is larger than the screen.
If you are not using Compiz (3D desktop effects) then you can hold down the Alt button and then left-click and drag the window around.
However if you have Compiz enabled then you may find the window does not want to go above the top of the screen. To enable you to move the window above the top of the screen you need to run the following command from the terminal. Make sure you run it as yourself (not root), additionally this is for the Gnome desktop environment:-
gconftool-2 --set /apps/compiz/plugins/move/allscreens/options/constrain_y --type bool 0
You should now be able to hold down Alt and left-click and drag your windows wherever you want.