<% %> 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.
<%= %> most useful for displaying single pieces of information.
<%# %> Data Binding Expression Syntax.
<%$ %> ASP.NET Expression.
<%@ %> Directive Syntax.
<%– –%> Server-Side Comments.
<%: %> Like <%= %> But HtmlEncodes the output (new with Asp.Net 4).
Direct copy from http://forums.asp.net/p/1139381/1828702.aspx