DeskPins can be used to make any application topmost, that is, to keep it above all other windows. Just grab a pin from the DeskPins icon in the system notification area (a.k.a. taskbar tray) and click on any window.Discontinued
The program seems to be no longer updated. Last version, 1.32, released in February 2015, can be still downloaded from the official website.
"Window On Top" is a small gadget made by Compzets.com which keeps any specific window on top of other windows. It does not have any user-interface (UI), it just sits on your tray bar and works with only a single keyboard shortcut.