At work we do code reviews as part of our development process. This means every commit has to have an additional set of eyes go over it and confirm the edits are good and adhere to the coding standards.
This can be an intrusive process, but also can be priceless. The creator of Python Guido van Rossum has developed a code review system whilst working for Google. The system is called Mondrian and there is some more information here on a blog interview. Currently it uses Perforce but in order for it to be released as open-source it will also work for Subversion and different database backends.