The system-wide default path is in
/etc/paths. The default on a 10.8 system contains the following:
To add additional system-wide
PATH entries, you could change that file, but a better option would be to add a file with the additional path entries to directory
/etc/paths.d. That user-created file will be protected during any upgrades/patches, which may replace a customised
/etc/paths with an Apple-distributed version.
Alternatively, you could put the appropriate
PATH modifying statements in
/etc/bashrc (in the case of bash, it will only use the latter if the former doesn't exist). Any other system-wide environment changes can be done using those files as well.
User-specific configuration can be put in
Note: In the above, I've assumed you're using bash - if you're using csh or zsh, you'll need to adjust their configuration files (the information about
/etc/paths.d remains valid, however).