Watermark applied using the majax.watermark Plugin

<asp:TextBox ID="TextBox1" runat="server" CssClass="watermark" ToolTip="First Name" />

Watermark applied using the AjaxControlToolkit's TextBoxWatermarkExtender Control

<asp:TextBox ID="TextBox1" runat="server" ToolTip="First Name" />
<ajaxToolkit:TextBoxWatermarkExtender ID="TextBoxWatermarkExtender1" runat="server" TargetControlID="TextBox1" WatermarkCssClass="watermark" WatermarkText="First Name" />