Here's something I found myself needing many times over the years. (Working on Windows 7 here.)
Sometimes I'll be working on my computer and having many windows open. So I use Alt-Tab to navigate between them. But the annoying thing is that sometimes Windows has windows that don't show up on alt-tab, like small dialogs. For example, try opening a folder in windows, selecting a file and pressing the Del button. Windows shows a dialog to delete the file. Now, say you've already switched to a different window and you have a mess of windows covering that delete dialog. Now say you want to navigate back to it. You try using alt-tab, but that delete dialog doesn't appear in the alt-tab window list!
My idea: A program that listens for win-alt-tab and shows an alt-tab window that scrolls through all those windows that aren't on the original alt-tab list. That way I could get to them without having to use the mouse and search for them visually.
If anyone feels like taking up this challenge, please let me know!