Tonight I uploaded the first release of Project Ubertooth, an open source wireless development platform that can be used for Bluetooth testing and research. This is a very preliminary release, but it includes the complete hardware design for Ubertooth Zero, firmware source code, and the host code needed to perform rudimentary Bluetooth sniffing as I demonstrated at ToorCon 12. Although you can download a project archive, I recommend using the Subversion repository so that you can easily keep up to date with the project as it develops.
The documentation is still a bit thin, but there are README files scattered about the project directories. The host code can be compiled with gcc on Linux. The firmware also can be compiled with a gcc toolchain (I have found the CodeSourcery package to be helpful) and can be flashed onto a board with lpc21isp. I've been using a slightly modified SparkFun FTDI Basic Breakout for this, but there are several serial programming devices that will work with lpc21isp.
Also in the repository is an early hardware design for Ubertooth One, the next generation board that I hope to have ready within a couple months. This is a more challenging design that will probably require a few revisions, so keep your expectations low if you try to build one based on the current layout.