I ran across this on eBay.

I began thinking...wouldn't this be cool to add touch sensors under the plastic casing of our robots and make them even more interactive?! Image it playing a particular script if touched under its "arms" or play a sound file when pet.

Here is an info grab of this particular device that only uses one input to read 8 sensors! (ignore the "A" word). Even if this one isnt compatible I know there are some capacitive sensors that are.

• Arduino interface shield that provides 8 capacitive touch detection circuits
• Interfaces to the Arduino through only one Arduino pin!
• Uses high speed, half-duplex soft serial' to communicate with the Arduino this let's you choose any Arduino pin for communication with the XCTS-8A.
• Arduino library for XCTS-8A is available for download
• Capacitive Touch Sense technology is a reliable alternative to mechanical switches - There are no moving parts to wear out or corrode over time
• Senses touch through any non-conductive material like glass, plexiglass, tile, wood, plastic, drywall, etc.
• Sensitivity of the Touch Sense circuitry is adjustable to support a wide range of overlay materials and thicknesses - up to 1" thick or more
• Create custom touch sense plates using any conductive material such as copper tape, copper clad board, or even some random small metal objects
• On-board LEDs provide visual feedback when touch is detected, 8 indicator LEDs display the state of the touch sense circuits Applications: Any application that calls for pushbuttons or toggle switches Invisible switch - hidden behind any non-conductive surface like tile, wood, drywall, etc. Replacement of mechanical pushbutton or toggle switches with reliable solid state Capacitive Touch switches Capacitive Proximity switch - sensitivity can be set high enough to detect the nearby presence of a person, animal, or any other object containing trace amounts of moisture. Moisture sensor switch - this circuit can detect the presence of moisture nearby (within 1/2") without having to come in direct contact with the moisture itself. This is an intermediate electronic kit containing 38 components and 1 PCB, and can be assembled in about 1 hour Designed and packaged in the USA