+1  A: 

Use the fully qualified name you want to use, e.g. Microsoft.Web.Mvc.ControllerExtensions.RedirectToAction() so that the compiler knows which one you want to call.

Lucero
+3  A: 

To complete Lucero answer,
If that seems a big drawback to you to use the fully qualified name (not very elegant), you can set a shorter alias to the namespace:

using MvcContrib;
using Future = Microsoft.Web.Mvc.ControllerExtensions; 

you can then write it Future.RedirectToAction() or just

RedirectToAction();

if you want to use the one from MvcContrib.

Of course you could just reverse this if you want to use primarily the futures assembly or the alternative to use the Contrib.

Hope this helps :)

Stephane