GravatarExtensions.cs

using System.Web.Mvc;

    public static class GravatarExtensions
    {
        public static MvcHtmlString Gravatar(this HtmlHelper helper, string email, string username, int size)
        {
            var baseURL = "http://www.gravatar.com/avatar/{0}?s={1}&d=identicon&r=PG";

            TagBuilder link = new TagBuilder("a");
            link.Attributes.Add("href", "/User/" + username);

            TagBuilder img = new TagBuilder("img");
            img.Attributes.Add("src", string.Format(baseURL, Helpers.Functions.MD5Hash(email), size.ToString()));
            img.Attributes.Add("alt", username);
            img.Attributes.Add("title", username);

            link.InnerHtml = img.ToString();
            return MvcHtmlString.Create(link.ToString());
        }
    }

Gravatar extension for ASP.NET MVC 2