Portal 2 Gels available at thinkgeek
Comes in Repulsion Gel, Propulsion, Gel, and white sticky Conversion Gel flavors. Course, they dont really do any of the things their digital vidya gaem counterparts do, but at least you have a great prop for all your future Companion Cube cosplaying oufits.
Um, no, this has no practical purpose. And yet it is still made of awesome.