Adding dynamic controls

I have always added dynamic controls like so:

Label l = new Label();
l.Text = "Label 1";

this.Controls.Add(l);

on Page_Load. But if I try to add a Button dynamically, I get an error saying it has to be nested in a <form>.

So I checked the HTML source and saw that the items I add dynamically are added below the end </HTML> tag!

How can I add the controls so they're between the <form></form> tags?

You basically need a container to hold it... unfortunatly the only things i know that can do this from code are Tables, Panels and Placeholders.