paultyng 

HTML 5 EditorTemplates for MVC 3 in Razor. A fork of skirkland's MvcHtml5Templates with additional functionality. Adds support for placeholder and required attributes among other additions.

A Fluent JSON library for building Knockout view models (or any other JSON object) built on top of JSON.NET.

Diff an object graph (for auditing or human readable purposes). Uses DataAnnotations so good for MVC sites.