So, when I switched to using two monitors for development, unfortunately, my Photoshop window got "stuck:" the top of it was off-screen, and thus I couldn't move it (and resizing it wouldn't help).
Google didn't help. :-|
What worked for me on OS X was:
- Open the system preferences.
- Go to displays.
- Go to "arrangement."
- Move the white "menu" bar from one of the displays to the other one.
...This "juxtaposed" the PS window (all windows, actually), and that brought back the top of the window and the ability to move it.