How to change PATH environment variable to OS X 10.8 Mountain Lion that will be visible to GUI applications?
With Mountain Lion /etc/launchd.conf is where you should set the GUI applications Path. Remember it's not a script file; it only supports launchctl commands so you should write something like:

setenv PATH /new/path:/usr/bin:/bin:/usr/sbin:/sbin


Note also that it doesn't support shell environment variable substitutions (like $PATH) so you'll have to set every path that you want to include. It's a good idea to keep the original paths that you've mentioned (/usr/bin:/bin:/usr/sbin:/sbin).

You'll have to reboot after changing (or creating) the file for the changes to take effect.