<asp:button id="btnID" runat="server" CssClass="button" Text="Save Current Screen Contracts"  UseSubmitBehavior="false" OnClientClick="this.disabled=true" />

http://weblogs.asp.net/jeffwids/archive/2009/10/06/how-to-disable-an-asp-net-button-when-clicked.aspx

this will disable a button after the first click, but will continue to do its original postback. Note: if it has a custom css class, then the button will still appear clickable, with the exception that the text of the button gets the slight disabled look. But in reality, it really is disabled.

Disable ASP.NET button on click (but still postback)

button

ASP