I heard of the Mozzi database of sounds for Arduino after reading a paper(1) from the ICAD 2013 (International Conference on Audio Displays) conference which referenced its creation and development.
“Currently your Arduino can only beep like a microwave oven. Mozzi brings your Arduino to life by allowing it to produce much more complex and interesting growls, sweeps and chorusing atmospherics.”
The example sounds are lovely, I particularly recommend ‘A chordal wash of detuned oscillator pairs’ which reminded me of something I might hear in a Radiolab podcast.
More at: http://sensorium.github.io/Mozzi/
(1) Stephen Barrass and Tim Barrass (2013) Embedding sonification in things [pdf freely available] ICAD 2013
“These experiments have led to the initiation of an open source sonification synthesizer project called Mozzi on github . You can download and freely use Mozzi under the open source license in your own embedded sonifications . You can also add your own extensions by forking the source. We hope that Mozzi will enable a wave of embedded sonifications.”
 Barrass, T. Mozzi Sound Synthesis Library for Arduino, retrieved 31 March 2013, http://sensorium.github.com/Mozzi/