What is the purpose of eyebrow windows?
Wikipedia answers this on the Boeing 737 page:


  Most 737 cockpits are equipped with "eyebrow windows" positioned above
  the main glareshield. Eyebrow windows were a feature of the original
  707 and 727. They allowed for greater visibility in turns, and
  offered better sky views if navigating by stars. With modern avionics,
  they became redundant, and many pilots actually placed newspapers or
  other objects in them to block out sun glare. They were eliminated
  from the 737 cockpit design in 2004, although they are still installed
  at customer request. These windows are sometimes removed and
  plugged, usually during maintenance overhauls, and can be
  distinguished by the metal plug which differs from the smooth metal in
  later aircraft that were not originally fitted with the windows.