Recording with contact microphones is fascinating territory to explore – inspired by the incredible work of Alan Splet and Anne Krober I started experimenting with a custom built Trance Audio Inducer contact mic and preamp back in 2001, and a couple of years later added a pair of Barcus Berry Planar Wave contact mics. This library is literally the result of hundreds of hours of experimenting and capturing uniquely malleable sounds.
One aspect of contact mic recording that is fascinating for sound design is the lack of acoustic – there is no reverb due to the sounds being recording via direct vibration, not through the air. This feature alone makes for very malleable sounds, excellent as components and layers in complex, composite sounds or for when you need an abstract organic sound but where the actual source must remain concealed…
For more details on techniques and set up, please see this blog post: The First Rule of Contact Mic CLub
For more info on using contact mics, check this post at The Music of Sound