I really believe in the open source philosophy and many of these modern free tools are just as good and sometimes even more powerful than many programs you could pay top dollar for. My work-flow for post processing is 100% open source, there’s simply a lot of great stuff out there.
Operating System: Ubuntu 12.04 (Precise Pangolin)64-bit PC (AMD64) desktop
Post-processing: GIMP 2.8.2
Additionally I use F-Spot for importing, file management, and quick viewing. Right clicking on the photo can open in GIMP or UFRAW
For the command line:
Metadata: Exiftool by Phil Harvey
You can do a lot with ImageMagick
Here are some of the scripts and plug-ins I am using. Details and reviews of which will come over time.