Top 20 NuGet client Packages

Json.NET web client
BLiP Extensions' extensions to include logs, including a TCP/HTTP ISender factory
Provides infrastructure for common authentication and additional convenience APIs for Azure REST clients.
.NET client for Neo4j Graph Database
LEGACY PACKAGE - Use GoogleAnalyticsTracker.WP7 or GoogleAnalyticsTRacker.WP8 instead - GoogleAnalyticsTracker was created to have a means of tracking specific URL's directly from C#. For example, it enables you to log API calls to Google Analytics.
Task Parallel Library (TPL) extension methods for Windows Azure Storage Client library
A .NET client for interacting with Zoho CRM service
AsyncParse.Net is a library to enable access to Parse.com through the asynchronously-capable Microsoft .NET Framework 4 HTTP Client Libraries
WebApiDoodle.Net.Http is a library which provides more features over System.Net.Http
WebApiDoodle.Net.Http.Client is an ASP.NET Web API library which contains several useful Extensions, Filters, Message Handlers and so on and so forth.
MobileGATracker was created to have a means of tracking specific URL's directly from C#. For example, it enables you to log API calls to Google Analytics.
A light-weight, async/non-blocking Memcached client for .NET
A simple synchronous/asynchronous REST client for .Net
JsonRPC Portable Class Library
A REST Client base for your .Net projects.
Client Library for the Coderbits API in Windows Store Apps
ElmahR Api client for extended ElmahR dashboard using a Nancy endpoint (https://github.com/ziyasal/ElmahR.Api.Nancy)