JCR is a Web application for performing and managing formal code reviews. Although it has some special logic for reviewing Java projects, it can be used for reviews of any type of source code. JCR manages all stages of the review process (initial project setup, individual review, joint review meeting, post-review tidy-up), but it's mainly there to show diff views of files that have changed and to allow comments to be made on any line of any file marked for review.
This version adds the ability to view diffs side-by-side, in addition to the existing unified (single column) view. There have also been several minor usability enhancements.
URL: JCR - Java Code Reviewer