Sophi Kravitz built a very interesting device called the Texting Trapper:
Texting Trapper knows when you are texting, calling or accessing the internet. This is a fun and interactive exhibit that measures the strength of your cell phone signal or radiation.
There's a nice series of posts on her blog describing the design of the cell phone detection circuitry. Of course, Maker Faire often throws unexpected hurdles at makers and such was the case for Sophi. She found that the RF levels in the exhibition hall were overwhelming the device. The solution: build a Faraday cage!
This last hack, the Electric Imp, allows any device with an SD card slot to become Internet connected. Cabe already wrote an informative post on this upcoming product. Here's a great interview with the creator, Hugo Fiennes, by Make's Matt Richardson:
As a computer history buff, I really dig the name, too, as it was named after the first model of Internet router, Interface Mesage Processor or IMP.