If the REST services were built using ASP.NET Web API then I would use the Microsoft Http Client Libraries. (nuget package available). N.B. This appears to have superseded the web api client libraries that are listed in the nuget screenshot on the link below.
This will work from .NET 4, Windows Store Apps, Windows Phone 7.5/8, Silverlight 4 and 5.
In theory you could use it to call any REST service built with other frameworks as well.
Here's a link with some samples on using the HttpClient class to call REST services:
Calling a web api from a .net client
