RestKit
Framework for consuming and modeling RESTful web resources
... contents into an array of Tweet objects. RestKit is designed to be modular and each module strives to maintain a minimal set of dependencies across the framework and with the host platform. At the core of library sits the object mapping engine, which is responsible for transforming objects between representations (such as JSON/XML <-> local domain objects). The object mapping engine is built on top of the Key-Value Coding (KVC) informal protocol.