asp.net dropdownlist – add blank line before db values

You can simply add a ListItem inside the DropDownList Markup. All the values from the DataSource will be appended after that.

<asp:DropDownList ID="drpClient" runat="server" Width="200px" 
          AutoPostBack="True" DataSourceID="dsClients" DataTextField="name" 
          DataValueField="client_id" AppendDataBoundItems="true">
   <asp:ListItem>-- pick one --</asp:ListItem>
</asp:DropDownList>