Make window always on top?

I use Deskpins for this:

There is also PowerMenu if you prefer a context menu solution, which lets you set application priority and transparency from the context menu as well:

Install AutoHotkey and use this script to toggle any window as topmost by pressing CTRL SHIFT T:

^+t::
      WinSet, AlwaysOnTop, Toggle,A
return

Ash's answer using AutoHotkey is a great alternative. However, the current state of the script can be troublesome. The AlwaysOnTop property is persistent even after AutoHotkey is no longer running. You could go through each window manually and toggle this property to off, but we're using AutoHotkey; We can do it automatically!:

!#Down:: ;Windows+Alt+Down
    WinGet, windows, List
    Loop, %windows%
    {
        window := windows%A_Index%
        WinSet, AlwaysOnTop, Off, ahk_id %window%
    }
    WinSet, AlwaysOnTop, On, ahk_class Shell_TrayWnd
return