Under 10.8 which file stores the environment variables? This has been this way since 10.6. There is no .bashrc file in the home dictionary but the environment variable PATH indeed exists as the result of this command shows:

$ echo $PATH
/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin


Anyone know how/where OS X stores environment variables?
The system-wide default path is in /etc/paths. The default on a 10.8 system contains the following:

/usr/bin
/bin
/usr/sbin
/sbin
/usr/local/bin

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/profile or /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 $HOME/.bashrc or $HOME/.bash_profile.
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 and /etc/paths.d remains valid, however).