The following AppleScript will move all windows which are offscreen to the main screen. This is useful when you have disconnected an external display, and the windows you had open on that screen (or screens) are now unreachable.
Copy and paste this code into Script Editor:
-- Example list of processes to ignore: {"xGestures"} or {"xGestures", "OtherApp", ...}
property processesToIgnore : {}
-- Get the size of the Display(s), only useful if there is one display
-- otherwise it will grab the total size of both displays
tell application "Finder"
set _b to bounds of window of desktop
set screen_width to item 3 of _b
set screen_height to item 4 of _b
end tell
tell application "System Events"
set allProcesses to application processes
set _results to ""
repeat with i from 1 to count allProcesses
set doIt to 1
repeat with z from 1 to count processesToIgnore
if process i = process (item z of processesToIgnore) then
set doIt to 0
end if
end repeat
if doIt = 1 then
tell process i
repeat with x from 1 to (count windows)
set winPos to position of window x
set _x to item 1 of winPos
set _y to item 2 of winPos
if (_x < 0 or _y < 0 or _x > screen_width or _y > screen_height) then
set position of window x to {0, 22}
end if
end repeat
end tell
end if
end repeat
end tellMac OS X Hints
http://hints.macworld.com/article.php?story=2007102012424539