The Backbone.js wagon is a pretty sweet wagon to be on right now. If you're just jumping in there is a learning curve and not much for documentation. Here are some compiled resources I've found to be helpful.
Backbone.js The official download and documentation site. This is what I reference the most.
Backbone Fundamentals An open source book on Backbone.js.
Common Backbone.js Error Messages A list of commonly seen Backbone error messages and what they mean. Money.
Backbone.js Design Patterns There are always more than one opinion on best practice, but this list of items is nicely laid out. Good beginner info.
Backbone.js Screencasts on Peepcode These videos are amazing as well as the source code. Really helped me.
CHRISTOPHE COENRAETS' blog This guy posts some cool examples using a number of technologies. He organizes some of his code with Backbone so if you don't have peepcode you can pull down one of this guys github repos and dig into some Backbone code.
A Funny Jasmine Walkthrough An entertaining blog about Jasmine.