<!-- The HTML -->
<div id="container">
   <div id="header"></div>
   <div id="body"></div>
   <div id="footer"></div>
</div>

<!-- The CSS -->
<style>
	html,body {
	   margin:0;
	   padding:0;
	   height:100%;
	}
	#container {
	   min-height:100%;
	   position:relative;
	}
	#header {
	   background:#ff0;
	   padding:10px;
	}
	#body {
	   padding:10px;
	   padding-bottom:60px;   /* Height of the footer */
	}
	#footer {
	   position:absolute;
	   bottom:0;
	   width:100%;
	   height:60px;   /* Height of the footer */
	   background:#6cf;
	}	
</style>

Footer (bottom)

HTML