I've also had a good experience using Knockout. I used it to add some interactivity to a largely static site, and then expanded its use to create a fairly complex management interface. It's easy to pick up with great interactive tutorials on the web site, and with component support in the latest version you can build some larger web apps.

Microsoft uses it their recent remake of their Azure portal; this page has a video on building large apps with Knockout: http://jbeckwith.com/2014/09/20/how-the-azure-portal-works/