There is a new version of original +mammon gdbinit, 7.0 (available at http://truthix.dump.cz/files/.gdbinit).
GDB version used by Apple has some problems with it (doesn’t recognize global variables outside each function) so it needed some fixes to work. I have changed the colors and removed the data window display (personally I don’t think it’s useful, edit “define context” and remove the comment for “datawin”).
Grab it here: gdbinit
If you want to see what was changed, just diff the two versions!
Update: Just ported version 7.1 dd fix to this version. Grab it here: gdbinit-7.1-macosx