One shortcut I missed when switching from Mac OS X back to XP was the ability to cycle the windows of an single app using Command+`.
When I upgraded to Windows 7, I was excited to see that it has this feature, kind of: You can ctrl+click on a grouped taskbar icon to cycle through the group. It works, but I hate having to use the mouse to do it. Before I go installing every shortcut mapper known to man, is there one that you know has the ability to map a key to this function?