<asp:GridView runat="server" id="grid" 
            AutoGenerateColumns="false" ShowFooter="true" >
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        valore: <%# Eval("campo") %>
                    </ItemTemplate> 
                    <FooterTemplate>
                        Totale: <%# (grid.DataSource as System.Data.DataTable).Compute("Sum(campo)",null) %>
                    </FooterTemplate>
                </asp:TemplateField>
            </Columns>    
        </asp:GridView>