There are all sorts of different inline tags, and I haven't found a place that explains them all in one place, so here is the quick and dirty...

<% ... %>

The most basic inline tag, basically runs normal code:

<% if (User.IsInRole("admin")) { %>  You can see this<% } else { %>  You are no admin fool!<%} %>

http://msdn2.microsoft.com/en-us/library/ms178135(vs.80).aspx

<%= ... %>

Used for small chunks of information, usually from objects and single pieces of information like a single string or int variable:

The Date is now <%= DateTime.Now.ToShortDateString() %>The value of string1 is <%= string1 %>

http://msdn2.microsoft.com/en-us/library/6dwsdcf5(VS.71).aspx

*note: <%= is the equivalent of Response.Write()

<%# .. %>

Used for Binding Expressions; such as Eval and Bind, most often found in data controls like GridView, Repeater, etc.:

<asp:Repeater ID="rptMeetings" DataSourceID="meetings" runat="server">
  <ItemTemplate>       
    <%# Eval("MeetingName") %>   
  </ItemTemplate>
</asp:Repeater>

http://msdn2.microsoft.com/en-us/library/ms178366.aspx

<%$ ... %>

Used for expressions, not code; often seen with DataSources:

<asp:SqlDataSource ID="party" runat="server" ConnectionString="<%$ ConnectionStrings:letsParty %>" SelectCommand="SELECT * FROM [table]" />

http://msdn2.microsoft.com/en-us/library/d5bd1tad.aspx

<%@ ... %>

This is for directive syntax; basically the stuff you see at the top your your aspx pages like control registration and page declaration:

<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Title="Untitled Page" %><%@ Register TagPrefix="wp" Namespace="CustomWebParts" %>

http://msdn2.microsoft.com/en-us/library/xz702w3e(VS.80).aspx

<%-- ... --%>

This is a server side comment, stuff you don't want anyone without code access to see:

<asp:Label ID="lblAwesome" runat="server" />   
<%-- sometimes end users make me angry --%>   
<asp:LinkButton ID="lbEdit" Text="Edit" OnClick="Edit_Click" runat="server" />

http://msdn2.microsoft.com/en-us/library/4acf8afk.aspx