"One of the hidden gems in ASP.NET 2.0 is the new expression syntax. For example, to display the value of a setting in the AppSettings section of your web.config, you can do this: 
<asp:Label Text="<%$ AppSettings:AnotherSetting %>"
    ID="setting" 
    runat="server" />

Notice that the value of the Text property of the Label control is set to an expression that is similar to the DataBinding syntax (<%#), but instead of a pound sign (#) it uses a dollar sign ($)." (haacked)

I implemented a code expression builder before so that I can use things like <%$ code: GetResult() %> in my template