Here's an 8-bit resistor DAC on Arduino Uno that I built during the weekend, playing a techno loop @ 16KHz. Not exactly the best audio quality, but it's my first own Arduino project (: Also recording the audio on iPhone doesn't help.
I had bunch of random resistors laying around so I measured resistance of each (~150 total) and wrote a small app that gave me the closest matching parallel resistor pair for each pin.