Meet IntelliCommand (Visual Studio 2010/2012 extension)

A free extension that can be downloaded from the Extension Manager within Visual Studio, that shows you all possible shortcut keys. It shows the help windows with all the possible combinations when you press Ctrl or Shift or Alt or their combinations. (hold it for about 2 seconds to see this window). Also it shows the list of possible combination when you press first combination of chord shortcut keys, like Ctrl + K, Ctrl + C (this combination comments selected text in editor).

To install, Open up Visual Studio, Click Tools -> Extension Manager. Then search for IntelliCommand inside the online Gallery.