• Military Vehicle Modelling by Phil Greenwood
  
  (The Crowood Press 2002)
  The first book I read on this subject – it taught me a lot. Perhaps you need to look elsewhere for advanced weathering techniques as the author seems not to be a huge fan of it.
• The Airfix Book of Scale Modelling by Jonathan Mock
  
  (Conway Publishing 2011)
  Another good book for a beginner – and expert too! Lots of interesting technical and historical information.
• Airbrushing and Finishing Scale Models by Brett Green
  
  (Osprey Publishing 2008)
  As the name suggests, very good at airbrushing techniques. Some nice armour examples.
• Small-Scale Armour Modelling by Alex Clark
  
  (Osprey Publishing 2011)
  Focuses on 1/72 scale but still relevant to other scales. Some awesome modelling inside.
• Advanced Terrain Modelling by Richard Windrow
  
  (Osprey Publishing 2007)
  Techniques are illustrated by way of various landscape projects.
• Terrain Modelling by Richard Windrow
  
  (Osprey Publishing 2001)
  Chapters are split up into creating various landscape types. A good companion to the above book.
• FAQ 2 by Mig Jiménez
  
  (AK Interactive 2011)
  Particularly strong on weathering effects – washes, streaks, stains, chipping, rust, mud, dust, oil …
• Modeling US Armor of World War 2 by Steven Zaloga
  
  (Osprey Publishing 2009)
  Very good general book by a master modeller – good chapter on photography and image manipulation.