I've patched together a few examples (including the very useful CultivSearchEngineSitemap) to make a sitemap that allows me to exclude docs by their type (I have a list of excluded types and am using a lamda expression to filter this. 

I added umbracoNaviHide to my master doc type but not all doc types are under this and to stop an exception being thrown I've added a check. The issue is that the umbracoNaviHide".Value != "1" doesn't seem to work - the pages where this true/false value is set still show in the sitemap output. Any ideas why?

I also failed in trying to find a way of excluding protected pages - this isn't important for this project but any pointers on this would be useful. 

@inherits Umbraco.Web.Macros.PartialViewMacroPage

@{
    Response.ContentType = "text/xml";
    var homepageContainerId = 1060;
    string[] excludeTypes = { "settings", "Historyitem"};

    var homepage = Umbraco.TypedContent(homepageContainerId);
    if (homepageContainerId != null)
    {
        @:<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
        // pages contains only bona fide pages - e.g. not content nodes that are just used to build up other pages 
        var pages = homepage.DescendantsOrSelf().Where(x => (!x.HasProperty("umbracoNaviHide") || (x.HasProperty("umbracoNaviHide") && x.GetProperty("umbracoNaviHide").Value != "1")) && !excludeTypes.Contains(x.DocumentTypeAlias));

        foreach (var page in pages)
        {
            <url>
            <testonly>@page.Name</testonly>
            <loc>@GetUrlWithDomainPrefix(page.Url)</loc>
            <lastmod>@(string.Format("{0:s}+00:00", page.UpdateDate))</lastmod>

            @if (page.HasValue("SearchEngineSitemapChangeFreq"))
            {
                <changefreq>@page.GetProperty("SearchEngineSitemapChangeFreq").Value</changefreq>
            }
            else
            {
                <changefreq>yearly</changefreq>
            }

            @if (page.HasValue("SearchEngineSitemapPriority"))
            {
                <priority>@page.GetProperty("SearchEngineSitemapPriority").Value</priority>
            }
            else
            {
                <priority>0.5</priority>
            }
            @if (page.HasProperty("umbracoNaviHide")) { 
                <ishiddenTEST>@page.GetProperty("umbracoNaviHide").Value</ishiddenTEST>
            }
            </url>
        }
        @:</urlset>
    }
}

@functions {
    private static string GetUrlWithDomainPrefix(string url)
    {
        if (url.StartsWith("/"))
            url = url.Substring(1);

        var domainPrefix = string.Format("http://{0}/", HttpContext.Current.Request.ServerVariables["HTTP_HOST"]);

        if (url.StartsWith(domainPrefix))
            return url;
        else
            return domainPrefix + url;
    }
}