http://hackaday.com/2014/10/17/detect-cosmic-rays-with-your-smartphone-using-crayfis/
I find this cosmic ray project very appealing.
Also, Adam Fabio over on Hackaday recently posted a Hack-let on ham radio:
http://hackaday.com/2014/10/17/hacklet-19-ham-radio/
Our book: “SolderSmoke — Global Adventures in Wireless Electronics” http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20