I've been thinking for a while of formalizing code reviews for the project I run. The free software options in this area seem to be pretty limited at this point. I had previously looked at Codestriker. Recently, Review Board came to my attention. It looks pretty promising.
Regardless of which solution I pick I'm going to have to do some work to integrate it with my project (which includes a revision control system), so I'd like to find one that I really like before embarking on that work.