Monk//Ranger? Not much synergy there aside from their ability requirements. Generally, in gestalt, you'll want at least one side to be a full caster class.

My suggestions: Cleric or Psychic warrior or Druid

Psywar is probably the best for flavour, since they're pretty martial and fit the theme of a monk pretty well. Just describe the psychic powers as chi or something and avoid the really supernatural ones that make you grow tentacles. Most of the powers are buffs anyway. Some of the psionic feats also let you run up walls, change your attacks to touch attacks, and jump really, really far. It's good stuff.