In the upcoming release of ASP.NET 4.0 they have introduce 2 really nice features for SEO, the first one is being able to progmattically add Meta Keywords and Description to the page:


Page.MetaDescription = "Foo";
Page.MetaKeywords = "Foo, Bar, Baz";


Which will render the following in the header:
<meta name="description" content="Foo" /> <meta name="keywords" content="Foo, Bar, Baz" />


The 2nd nice feature added to ASP.NET 4.0 is 301 permanent redirects via the Response.RedirectPermanent("page.aspx") method. So now in your Global.asx.cs you can manage 302 redirects for pages who have moved like this:


protected void Application_BeginRequest(object sender, EventArgs e)
{
    if (Request.FilePath == "/Product/23.aspx")
    {
        Response.RedirectPermanent("/Products/23/", true);
    }
}

This gives you the ability to easily manage files that are indexed in a search engine but have moved progrmatically rather than doing it through your webserver (which is much better for people who are using shared hosting).