Sublime Text 2 Keybinding to Allow Shift + Space Exit Insert Mode.

Default (OSX).sublime-keymap

[
  { 
    "keys": ["shift+space"], 
    "command": "exit_insert_mode", 
    "context": [
      { "key": "setting.command_mode", "operand": false },
      { "key": "setting.is_widget", "operand": false }
    ]
  }
]