You can try using phabricator. It can be used for SVN and Git. It does a lot more but it does provide code review (before) and code audit (after).
I have been evaluating Gerrit, Reviewboard and Phabricator myself and have not yet decided which way to go.
A quick summary
Gerrit
Used by Android for example, so can't be bad
Supports only Git
Review is created by pushing to a special branch
Two methods of voting, verified (by Jenkins for example) and code review
After review the change can be pushed directly to the master branch by Gerrit
Comprehensive access control mechanism to protect the repository
UI not so attractive but fast, shows one file at the time
As it only shows one file at the time it has a nice tick box next to the files you have reviewed
Able to trigger Jenkins for verification of the patch
Written in Java (.war)
Very active development
Reviewboard
Used by Apache for example, so can't be bad
Supports any modern SCM
Pre commit and post commits reviews are created using a Python script
After pre commit review you can commit your code to the repository, however this is difficult to verify and can be by passed
No access control mechanism for repository as it is not under its control
UI is nice, but very slow when loading diffs. It can take a fair bit of time on my test system to load the file differences while Gerrit and Phabricator are much faster
Written in Python
Active development
Phabricator
For example used by Facebook and Dropbox, so can't be bad
Supports Git, Subversion and Mercurial
Pre-commit review by using php scripts
Post-commit reviews (audit) can be created by making rules that will trigger an audit (nice!)
Is more like a complete eco system which includes a bug tracker, repo browser, wiki and more
They call it light hearted, heavy duty. This means you need to put up with terms like "Clowncopterize" or "Avast" instead of "OK" and you can close tasks "Out of Spite"
Written in php
Very active development
My general impression is that Gerrit is favored by new open source projects, Reviewboard by older projects and Phabricator by new startups.