Review board

At the company (Navtech) I work for, I introduced a code review tool called "Review Board". An open source tool mainly developed
by vmware and used by many companies such as Google (Google Code Summer), Yahoo, Vmware,..
And now, my team and our adjacent team use it as well.
Very neat! Subversion integration, neat diff rendering (syntax highlighting), and the possibility to have good discussions about lines of code make it a very good tool for code reviews.