public static void ExportReportToPDF(HttpContext context, Microsoft.Reporting.WebForms.ReportViewer rViewer)

    {

        Microsoft.Reporting.WebForms.Warning[] warnings;

        string[] streamids;

        string mimeType = "";

        string encoding = "";

        string extension = "";

        byte[] bytes = rViewer.LocalReport.Render("PDF", null, out mimeType, out encoding, out extension, out streamids, out warnings);

        context.Response.Buffer = true;

        context.Response.Clear();

        context.Response.ContentType = mimeType;

        context.Response.AddHeader("content-disposition", "outline; filename=myfile." + extension);

        context.Response.BinaryWrite(bytes);

        context.Response.Flush();

    }

Para exportar para excel, basta alterar de:

 byte[] bytes = rViewer.LocalReport.Render("PDF", null, out mimeType, out encoding, out extension, out streamids, out warnings);

para:

 byte[] bytes = rViewer.LocalReport.Render("Excel", null, out mimeType, out encoding, out extension, out streamids, out warnings);