EasyNetwork - is powerful and easy-to-use http library for Android.
Helium is a DSL for REST API specifications and also a Java API for processing descriptions written in this language. The main goal of this project is to create a single source of truth about some REST API. Taking a spec as an input, Helium generates a lot of useful staff that can be used to rapidly develop REST clients.
Android Http Service is probably the easiest way of using RestServices with Android.
With this component you only have to define whatever you want before and after the request, and declare an intent in your manifest. It will handle network problems, verbs, headers etc. only giving them to it. Developers only have to tell the component what they want to send.