One of my rules for blogging is that I spend more than 15 minutes searching for something I should do a post that will help someone else in the future.
I am using a second monitor attached to my laptop when I'm at the office. I'm able to put everything (mail, IM, firefox, etc) on the second monitor and just keep Visual Studio and IE open for development on my main screen. Fantastic productivity enhancer. Except this is a laptop so when I'm connecting from somewhere else, and I'm don't carry a second monitor with me, windows will sometimes open in the phantom window, rendering them useless. Side note: I bet most people with laptops don't realize that they can probably do this with their relatively new machines. I think the assumption is that the monitor input is just for projectors and won't function as a second display. You should check. Monitors are cheap and you might even have an extra one around.
Lifehacker has a trick that works maybe 70% of the time here, but many windows don't have the "move" handler that this trick relies on.
I had discovered this one other time in my life, but it must have been pre-blog. It took me forever to find, but here is a very simple (crude) tool that will bring back any window. Also works in Vista, unlike a shareware tool I tried for this problem (Shove-It).
Force Window Visible
Future Google searchers, maybe this will help:
Restore off screen windows
Force windows on screen
relocate windows multi monitor tool
relocate lost windows
windows off screen
Help, I used to have a second monitor, now I can't find my windows