The Facepunch API is now almost ready for public consumption. I've just written up some basic documentation and had cosmic duck throw a site together for it.
You can now view the documentation and use the shiny new API console at the following address: http://facepun.ch
Please post any bug reports or suggestions in this thread so I can keep track of them. Any improvements to the documentation are also welcome.
If you're interested in developing an application based on the API, feel free to add me on Steam, and I'll be happy to answer questions regarding the API there too.