ActionResult is an abstract class that can have several subtypes.
ViewResult - Renders a specifed view to the response stream
PartialViewResult - Renders a specifed partial view to the response stream
EmptyResult - An empty response is returned
RedirectResult - Performs an HTTP redirection to a specifed URL
RedirectToRouteResult - Performs an HTTP redirection to a URL that is determined by the routing engine, based on given route data
JsonResult - Serializes a given ViewData object to JSON format
JavaScriptResult - Returns a piece of JavaScript code that can be executed on the client
ContentResult - Writes content to the response stream without requiring a view
FileContentResult - Returns a file to the client
FileStreamResult - Returns a file to the client, which is provided by a Stream
FilePathResult - Returns a file to the client
原文：http://www.cnblogs.com/Linford-Xu/p/3896361.html