The source code for RepRap is hosted on SourceForge.
It can be accessed (using subversion) at https://svn.sourceforge.net/svnroot/reprap/trunk/reprap
It is moderately large. To get just the source code, check out https://svn.sourceforge.net/svnroot/reprap/trunk/reprap/host and https://svn.sourceforge.net/svnroot/reprap/trunk/reprap/firmware
More information is available from the SourceForge subversion page
You can browse the current version of the source code
Alternatively you can download a tarball (4MB) with all the software in from here
-- Main.SimonMcAuliffe - 05 May 2006