void Application_BeginRequest(object sender, EventArgs e)
{
    HttpContext context = HttpContext.Current;
    string path = context.Request.Path;

    if (path.Contains(".aspx"))
    {
        if (path.ToLower().Contains("/article/"))
        {
            string id 
             = path.Remove(0, path.LastIndexOf("/") + 1).Replace(".aspx", "");

            try
            {
                int.Parse(id);
                context.RewritePath("~/article/article.aspx?ArticleID=" + id);
            }
            catch
            {
                // don't do anything because it's a postback
            }
        }
    }
}

It's fairly simple to follow. First, I checked to see if it was an ASPX page, so I can weed out all the HTTP Handlers being used. Then I checked if it's a page I want to manipulate. Essentially, what Context.RewritePath does is take the incoming URL and modify it before it hits the page handler. So when I go to /Article/3.aspx, the code see's that it contain's both '.apsx' and 'article', and then because I know the format, I am stripping off everything else and keeping the article ID. Once that is done I pass the ID to the page that actually get's called behind the scenes. It's a quick and dirty way to make URL's human-friendly.