Positive Grid's Accutune is a chromatic tuner designed to pickup sound via your iOS mic or via a USB guitar adapter.
Accutune gives you a responsive 25 cent range of fine tuning, with precision of up to ±1/100 semitone (±1 cent).
Just launch the app on your iPad or iPhone and it will listen to your instrument via the built in microphone of your iOS device. For quiet tuning, you can utilize an iOS guitar adapter like iRig or Positive Grid's JamUp Plug.
Accutune gives you two different views for excellent visual confirmation. The top portion of the screen shows a standard meter display while the bottom part features a nifty note-wheel. Both visuals give you good level of detail for easy tuning. You can calibrate the tuner from the default 440 Hz on the settings menu, you can also set transposition, adjust temperament and other settings.