A full featured SDR capable of transmitting (based on hackrf).
Which, to my knowledge, is the first time a conference has handed out badges that were actually useful afterwards. Pretty awesome.
And here's the talk: https://media.ccc.de/browse/conferences/camp2015/camp2015-68...
There was a talk about how this badge was built (non-comercially); it was only possible with most of the chips sponsored and a few people doing pretty much nothing else for months.