Reviewlead is an easy and lightweight code review tool.

You can find the product page here:
http://www.bytelead.be/products.php#reviewlead

You can see several examples (without login or registration) here:
http://www.bytelead.be/reviewlead/team.php?team=pieter

Or, you can just play around and create some reviews here (login/password = sandbox):
http://www.bytelead.be/reviewlead

Best regards
Pieter Beyens
Bytelead
http://www.bytelead.be