ActiveWindow Control Plasmoid
This KDE4 plasmoid lets you control the active window. Actions currently available : Close, Minimize, Maximize, Shade/Unshade, KeepAbove, KeepBelow. It was created at first to help users with KDE4 on small devices (it's easier to click on a big button...) but it is actually great even with a standart computer (just throw your cursor at the corner of the screen to close your window, buttons are always located in the same place on the screen, etc.).