Current maps:

Open the Istanbul public transport network in Google Earth.

(Help|Source)

• 
  topological map
• 
  schematic map
• 
  map of the districts of Istanbul
• 
  Metrobüs route map
• 
  Metrobüs lines
• 
  Metrobüs route statistics

• 
  stations of metro line M1
• 
  stations of metro line M2
• 
  stations of metro line M3
• 
  stations of metro line M4

• 
  Metro etc.
• 
  Metrobüs

Older maps (not longer maintained):

• 
  2006: existing routes only
• 
  2006: including planned routes
• 
  2006: svg Version
  (derivative work by Mortadelo2005)
• 
  2007: including planned routes
• 
  2010: schematic map without Metrobüs