We use plain GPG-encrypted files stored in our version control system (git/svn). The files get encrypted with all the public keys of the users who have access to these files, and can be decrypted with their private keys then. Not perfect, but works.
None of us are fluent enough in GPG practices to do this stuff off the top of our heads, though, so our management of these files involves a lot of rote "here's how to re-encrypt the file" or "here's how to import the new guy's key" instructions. It's pretty clunky.
Assuming you've all the public keys in your keychain, then for each key you pass "-r <email>" for the encryption, like "gpg -e -r foo@bar.com -r baz@bar.com plain.txt", and for decryption you do something like "gpg --output plain.txt -d plain.txt.gpg".
[0]: http://security.stackexchange.com/questions/8245/gpg-file-si...