Guido van Rossum, a Google App Engine developer, has released into open source the Rietveld Code Review Tool at http://codereview.appspot.com. This web application ties into a subversion repository to create a work flow for the review and commenting of newly submitted code.
This tool was born from an Google internal tool that Guido developed called Mondrian. Guido gave a Google TechTalk on the Mondrian tool called Mondrian Code Review On The Web (YouTube link). This TechTalk provides insight into how the work flow operates and how helpful a tool like this can be. Perhaps something to play with on your next project…
Overview of Rietveld Code Review Tool
Rietveld Code Review Tool online Demo
Mondrian Code Review on the Web (Google TechTalk Video)