Free RAW processors include:

UFRaw

Linux, Windows, Mac, BSD...

http://ufraw.sourceforge.net/

RawTherapee

'stable' version is 2.4.1 (now considered obsolete); the beta versions of 3.0 are pretty solid now. For Windows and Linux, Mac in the works.
http://rawtherapee.com/
v3 - for Windows, keep an eye on this thread:
http://www.rawtherapee.com/forum/viewtopic.php?t=1910
v3 for Linux:
http://www.rawtherapee.com/forum/viewtopic.php?t=2458
v3 for Mac:
http://rawtherapee.com/forum/viewtopic.php?t=2625

Roll (compile) you own:
http://www.rawtherapee.com/...p?f=10&sid=0c29146f838314b43874f5694b23f5…

How to use:
http://www.rawtherapee.com/forum/viewtopic.php?t=2507
http://code.google.com/p/rawtherapee/wiki/RT30ToolsetSummary

Darktable

Darktable is free, too (Windows and Linux; Mac port currently not maintained).
http://darktable.sourceforge.net/
To see it in action:
http://blog.pcode.nl/2010/12/06/darktable-0-7-screencast-library/

Photivo

Photivo is multi-platfrom (Windows, Linux, Mac) and free. Branched from PerfectRaw (now unmaintained), I think.
http://photivo.org/

RawStudio

Works on Linux only:
http://rawstudio.org/