The following is a rapid installation of PHP 5.5 on OS X 10.8. This compiles 5.5 from source, including two required libraries and finding the appropriate configure command. If you are comfortable at the command line, and especially if you are comfortable compiling your own binaries, then this should take no more than 30 minutes, with the majority being the actual PHP compilation.
Let's jump right in. Here's an overview of the steps: