I use two ways to manage paths in Mac OS X:
I use the first option when trying things out, and the second for managing the path more permanently.
And example of the using /etc/paths.d to include the git executable in PATH:
- edit /etc/paths.d/git
- Add line: /usr/local/git/bin
When you start a new Terminal session, the files under /etc/paths.d are read, and all paths found are appended to the PATH variable.