Shortcuts for the application switcher in OS X
What about the shortcuts to actually go left / right (i.e. choose different applications) within the application switcher?
  


Release the Command+Tab keys when the highlight is on a selected app to switch to that highlighted app or with the Command key still pressed:


tab – move selection to the right in the app list 
` – move selection to the left 
h – hide the selected application
q – quit the selected application 
mouse scrollwheel – move the selection back and forth
left arrow – move selection to the left 
right arrow – move selection to the right
up arrow – enter expose (Mission Control) within the selected application 
down arrow – enter expose (Mission Control) within the selected application


Source: http://osxdaily.com/2009/11/17/secrets-of-the-command-tab-mac-application-switcher/