3M Z-Axis Conductive Tape 9703 - 2"x6" (50mm x 150mm) Strip is made by 3M, and is used to bond two conductive surfaces together and allow a small (it’ recommended to keep it under 100mA) current to flow through the tape. The coolest part is it only conducts across the thickness of the tape itself, not along the length or width. There’s a macro shot of the tape above so you can see how it works. It’s a regular adhesive tape with little chunks of conductive material every 0.1mm or so. The adhesive does the bonding and the little chunks do the conducting.
Adafruit Web Site: http://www.adafruit.com/products/1656