Knockoutjs-vs-backbonejs is a project mainly written in ..., it's free.
ASP.NET MVC 3 (RC2) Project presenting a comparison between Knockout.js and Backbone.js
A side by side look at 2 client side frameworks who share similar goals but achieve it by different strategies. To be followed up with a blog post.
Although the title is slighty provactive it is not intended to suggest that one is in any way better than the other :)