Propellerheads' Gigantic Outdoor Drum Machine.

Propellerhead's outdoor drum machine that was taken out "in the wild" at night in Stockholm, Sweden, for people to play with! There are two songs in the video, both of the demo tracks that ship with Reason 5.0. The first one is Polyform by Sharooz Raoofi and towards the end you hear a piece of Kretsloppstest by Adam Beyer & Cari Lekebusch.
I especially like that the team used Phidgets to create this drum machine. Phidgets enable you to hook up a mix of digital or analog sensors to a USB interface. According to a post on Create Digital Music, the interface below was supported by a Phidget 8/8/8 interface hooked to a computer, and a force sensor under the pad. The team used a Phidget Voltage divider to make the scaling and calibration magic happen.

"Phidgets are a set of "plug and play" building blocks for low cost USB sensing and control from your PC. All the USB complexity is taken care of by our robust API. Applications can be developed quickly by programmers using their favorite language: C/C++, C#, Cocoa, Delphi, Flash AS3, Flex AS3, Java, LabVIEW, MATLAB, Max/MSP, MRS, Python, REALBasic, Visual Basic.NET, Visual Basic 6.0, Visual Basic for Applications, Visual Basic Script, and Visual C/C++/Borland.NET. Click on Programming if you want to look at Getting Started Guides or Code Samples."