Beyond 12 pitches

[ComposerOfAvantGarde]

This piece by Catherine Lamb is quite slow paced but really engaging at the same time.

https://www.youtube.com/v/jAN3yCtlkf0

From her website it says:

She studied (experimental) composition at the California Institute of the Arts (2004-2006) under James Tenney and Michael Pisaro, who were both integral influences. It was there also that she began her work into the area of Just Intonation, which became a clear way to investigate the interaction of tones and ever-fluctuating shades, where these interactions in and of them-selves became structural elements in her work.

which is probably just a bit of background info about her interest in using microtones in this way.

[wolftone]

George Friedrich Haas' string quartet 2 (and probably others) uses frequencies not found in 12-TET.

http://www.youtube.com/v/gnDmycfIweI

[listener]

and Some South-Paw Pitching
https://www.youtube.com/watch?v=igyvwAmsR_0