The good news is that in VS 2010 .Net 4, you'll have complete control over Client IDs!
Still for the current versions of .Net, you can make due. I assume you need the ID for JavaScript. If so, just get the ID like so:
<script type="text/javascript">
var myTextBox = $('#<%=TextBox1.ClientID%>');
</script>
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…