you might try Review Board: http://www.review-board.org/ which was developed by a couple of the coders at VMWare. It's now in use by several big and small companies, from Cisco and Motorola to Twitter and Meebo.
I'm not a big fan of Review Board for the following reasons:
- It's not effective for large changes because it presents all the diffs on a single page
- It makes it difficult to jump around in the code. I prefer being able to open the code in my editor of choice and jump around in the file using ctags or whatever code-navigation solution you use
- I would like better code-navigation features
It's not a bad tool, but my team didn't find it very well-suited to its needs
I looked at review board yesterday, and didn't really like how well it integrated. It seemed like there was a lot of manual patch creation. I'd prefer something that monitors the repository, automatically creates reviews, and sends them out to a group of people.
I can get close with Crucible, I'm currently looking into that a bit more.
EDIT: Also, supports subversion and git.