Also the rather neat Information Leakage from Optical Emanations[1], which demonstrated the ability to read data from networking equipment based on the state of the Rx/Tx LEDs on the front panel. In a lot of cases, the LEDs were being updated for individual bits sent and received.

I can't remember where I came across it, but there was a vendor with an advisory of something like "Mitigation Strategy: Cover Indicator LEDs with light-insulating tape".

Edit: Just remembered about the demo of an attack against signals radiated by (non-wireless) keyboard leads, and their detection and decoding: http://lasecwww.epfl.ch/keyboard/

[1] http://applied-math.org/acm_optical_tempest.pdf (PDF, obviously)