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() - Courtesy of Adam from the US,thanks!
<%# .. %>
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
And that's that.