I just found a little gadgety program for Windows named Y’z Shadow: all it does is add a little shadow effect to your windows (similarly to Mac OS X’s window shadow). While it sounds gimmicky, it’s amazing just how much difference a little shadow makes in distinguishing one window from the next. Try it out and see if it makes window management just that little bit easier for you!

Update: It looks like the YzShadow link above is dead, but you can appear to download it from at least one other website.