Recently I have been interested in interfaces that explore the use of silicon and its properties to achieve new and interesting interaction effects and applications. These are some that I was able to find so far.
1. Gel Sight by Micah Kimo Johnson which was shown at Emerging Technologies exhibition at Siggraph 2009 (thanks Ronit).
2. PhotoelasticTouch by the team from University of Electrocommunication was also shown at Emerging Technology exhibition at Siggraph 2009 (thanks Chris).
I am sure there is more and I would appreciate any additional pointers.