Over the holiday I had a little time to fiddle with the Raspberry Pi I got earlier in the summer and I started wondering how hard it would be to get a Bluetooth LE adapter working. It turned out not to be as hard to get working as I thought it might be thanks to recently added support in the Bluez 5.x Bluetooth stack. What follows is the information you need to get things going.
To start with I picked the IOGEAR Bluetooth 4.0 USB Micro Adapter (GBU521) that can be found on Amazon for just $13 since it looked like the chip it uses is decently supported with recent Linux kernels. The only issue I had is the size itself, if it didn't have a little nub on the end it would be too small to pull back out of the USB plug.