ASP.Net special tags

<% %> An embedded code block is server code that executes during the page's render phase. The code in the block can execute programming statements and call functions in the current page class.http://msdn2.microsoft.com/en-gb/library/ms178135(vs.80).aspx
<%= %> most useful for displaying single pieces of information.http://msdn2.microsoft.com/en-us/library/6dwsdcf5(VS.71).aspx
<%# %> Data Binding Expression Syntax. http://msdn2.microsoft.com/en-us/library/bda9bbfx.aspx
<%$ %> ASP.NET Expression. http://msdn2.microsoft.com/en-us/library/d5bd1tad.aspx
<%@ %> Directive Syntax. http://msdn2.microsoft.com/en-us/library/xz702w3e(VS.80).aspx
<%-- --%> Server-Side Comments. http://msdn2.microsoft.com/en-US/library/4acf8afk.aspx
<%: %> Like <%= %> But HtmlEncodes the output (new with Asp.Net 4).http://weblogs.asp.net/scottgu/archive/2010/04/06/new-lt-gt-syntax-for-html-encoding-output-in-asp-net-4-and-asp-net-mvc-2.aspx

Source: http://forums.asp.net/p/1139381/1828702.aspx
http://quickstarts.asp.net/QuickStartv20/aspnet/doc/pages/syntax.aspx