This is one of the best amplifier ICs I've used -
there is no noise (well barely any)
it has a built in digital volume control so you can just use a single gang pot to control the volume (or a microcontroller if you want)
it has an on/off switch that fades the audio in and out so you don't damage your speakers/headphones with pops and it is also very low voltage 3volts - 6volts
the only downside is the max rating is 6 volts so you can't just whack a 9v battery in it -
but 2 - 3 AAs and you're laughing.
I built this to use with my iPod but I strongly advise that you don't turn it on with your headphones on because this goes VERY loud. easily loud enough to damage your hearing instantly!