_Flash.cshtml

<div id="flash-messages" class="alert" style="display:none;">    
    <a class="close" href="#">&times;</a>
    <p></p>
</div>

<script type="text/javascript">
    $(function () {
        $("#flash-messages").flashMessage();
    });
</script>

_Layout.cshtml

@Html.Partial("_Flash")

ExampleController.cs

// Usage within MVC Controller
[HttpPost]
public ActionResult Create()
{
  return RedirectToAction("Index").Success("Message shown to user after redirect");
}

FlashMessageExtensions.cs

internal static class FlashMessageExtensions
{
    public static ActionResult Danger(this ActionResult result, string message)
    {
        CreateCookieWithFlashMessage(Notification.Danger, message);
        return result;
    }

    public static ActionResult Warning(this ActionResult result, string message)
    {
        CreateCookieWithFlashMessage(Notification.Warning, message);
        return result;
    }

    public static ActionResult Success(this ActionResult result, string message)
    {
        CreateCookieWithFlashMessage(Notification.Success, message);
        return result;
    }

    public static ActionResult Information(this ActionResult result, string message)
    {
        CreateCookieWithFlashMessage(Notification.Info, message);
        return result;
    }

    private static void CreateCookieWithFlashMessage(Notification notification, string message)
    {
        HttpContext.Current.Response.Cookies.Add(new HttpCookie(string.Format("Flash.{0}", notification), message) { Path = "/" });
    }

    private enum Notification
    {
        Danger,
        Warning,
        Success,
        Info
    }
}

jquery.cookie.js

/*!
 * jQuery Cookie Plugin v1.4.0
 * https://github.com/carhartl/jquery-cookie
 *
 * Copyright 2013 Klaus Hartl
 * Released under the MIT license
 */
(function (factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as anonymous module.
        define(['jquery'], factory);
    } else {
        // Browser globals.
        factory(jQuery);
    }
}(function ($) {

    var pluses = /\+/g;

    function encode(s) {
        return config.raw ? s : encodeURIComponent(s);
    }

    function decode(s) {
        return config.raw ? s : decodeURIComponent(s);
    }

    function stringifyCookieValue(value) {
        return encode(config.json ? JSON.stringify(value) : String(value));
    }

    function parseCookieValue(s) {
        if (s.indexOf('"') === 0) {
            // This is a quoted cookie as according to RFC2068, unescape...
            s = s.slice(1, -1).replace(/\\"/g, '"').replace(/\\\\/g, '\\');
        }

        try {
            // Replace server-side written pluses with spaces.
            // If we can't decode the cookie, ignore it, it's unusable.
            // If we can't parse the cookie, ignore it, it's unusable.
            s = decodeURIComponent(s.replace(pluses, ' '));
            return config.json ? JSON.parse(s) : s;
        } catch (e) { }
    }

    function read(s, converter) {
        var value = config.raw ? s : parseCookieValue(s);
        return $.isFunction(converter) ? converter(value) : value;
    }

    var config = $.cookie = function (key, value, options) {

        // Write

        if (value !== undefined && !$.isFunction(value)) {
            options = $.extend({}, config.defaults, options);

            if (typeof options.expires === 'number') {
                var days = options.expires, t = options.expires = new Date();
                t.setTime(+t + days * 864e+5);
            }

            return (document.cookie = [
				encode(key), '=', stringifyCookieValue(value),
				options.expires ? '; expires=' + options.expires.toUTCString() : '', // use expires attribute, max-age is not supported by IE
				options.path ? '; path=' + options.path : '',
				options.domain ? '; domain=' + options.domain : '',
				options.secure ? '; secure' : ''
            ].join(''));
        }

        // Read

        var result = key ? undefined : {};

        // To prevent the for loop in the first place assign an empty array
        // in case there are no cookies at all. Also prevents odd result when
        // calling $.cookie().
        var cookies = document.cookie ? document.cookie.split('; ') : [];

        for (var i = 0, l = cookies.length; i < l; i++) {
            var parts = cookies[i].split('=');
            var name = decode(parts.shift());
            var cookie = parts.join('=');

            if (key && key === name) {
                // If second argument (value) is a function it's a converter...
                result = read(cookie, value);
                break;
            }

            // Prevent storing a cookie that we couldn't decode.
            if (!key && (cookie = read(cookie)) !== undefined) {
                result[name] = cookie;
            }
        }

        return result;
    };

    config.defaults = {};

    $.removeCookie = function (key, options) {
        if ($.cookie(key) === undefined) {
            return false;
        }

        // Must not alter options, thus extending a fresh object...
        $.cookie(key, '', $.extend({}, options, { expires: -1 }));
        return !$.cookie(key);
    };

}));

jQuery.flashMessage.js

$.fn.flashMessage = function (options) {
    var target = this;
    options = $.extend({ timeout: 3000, alert: 'info' }, options);

    if (!options.message) {
        setFlashMessageFromCookie(options);
    }

    if (options.message) {
        $(target).addClass("alert-" + options.alert.toString().toLowerCase());

        if (typeof options.message === "string") {
            $('p', target).html("<span>" + options.message + "</span>");
        } else {
            target.empty().append(options.message);
        }
    } else {
        return;
    }

    if (target.children().length === 0) return;

    target.fadeIn().one("click", function () {
        $(this).fadeOut();
    });

    if (options.timeout > 0) {
        setTimeout(function () { target.fadeOut(); }, options.timeout);
    }

    return this;

    // Get the first alert message read from the cookie
    function setFlashMessageFromCookie() {
        $.each(new Array('Success', 'Danger', 'Warning', 'Info'), function (i, alert) {
            var cookie = $.cookie("Flash." + alert);

            if (cookie != "null") {
                options.message = cookie;
                options.alert = alert;

                deleteFlashMessageCookie(alert);
                return;
            }
        });
    }

    // Delete the named flash cookie
    function deleteFlashMessageCookie(alert) {
        $.cookie("Flash." + alert, null, { path: '/' });
    }
};

Updated for jQuery Cookie Plugin v1.4.0 and Bootstrap 3.0.3

Made some change to show multiple message like below.

return RedirectToAction("DashBoard", "agent").Danger("Danger message.").Success("this is a success").Warning("it's a warning");

https://gist.github.com/13orno/d44d0117f17bcd9d0cb7

Hello, Thanks for the code. Could you specify the license terms if someone want to use the code?

Thanks