How can I move mulitple windows at once to another monitor?

There are programs out there that can move all open windows to one monitor simultaneously. Display Fusion is one that I know of. However, unless you want all windows moved, you are going to have to go through them one at a time and select the ones you want moved anyway.

Using WinShiftLeft or WinShiftRight will move each window to the next or previous monitor and retain its relative position. You could move several windows over very quickly using this method, without having to move all of them.