It explains How to create a sidebar or section that follows you as you scroll down the page. It is very useful to show special or important content to user.

HTML:

<div id="wrapper">
      <div id="header"> ... </div>
			<div id="contentHolder"> 
				<div class="leftsidebar">...</div>
				<div class="content">...</div>
			</div>
      <div id="footer">...</div>
</div>

The main objective is to create fixed leftsidebar during scrolling between header and footer.

CSS:

#wrapper {
    margin: 0 auto;
    width: 1000px;
}
#contentHolder{
position:relative;
}
#header,#footer {
    background: none repeat scroll 0 0 #CCFFFF;
    color: #000000;
    height: 80px;
    width: 1000px;
	clear:both;
	font-size:3em;
	text-align:center;
	padding-top:20px;
}
.leftsidebar {
    background: none repeat scroll 0 0 #FFFFFF;
    border-color: #CCCCCC #BBBBBB #888888;
    border-style: solid;
    border-width: 1px 2px 2px 1px;
    margin-bottom: 3px;
    position: absolute;
    top: 0;
	width: 160px;
}
.leftsidebarfixed {
    position: fixed;
    top: 0;
}
.content {
    float: left;
    margin-left: 165px;
    position: relative;
    width: 570px;
}

jQuery:

$(function () {
  
  var msie6 = $.browser == 'msie' && $.browser.version < 7;
  
  if (!msie6 && $('.leftsidebar').offset()!=null) {
    var top = $('.leftsidebar').offset().top - parseFloat($('.leftsidebar').css('margin-top').replace(/auto/, 0));
	var height = $('.leftsidebar').height();
	var winHeight = $(window).height();	
	var footerTop = $('#footer').offset().top - parseFloat($('#footer').css('margin-top').replace(/auto/, 0));
	var gap = 7;
    $(window).scroll(function (event) {
      // what the y position of the scroll is
      var y = $(this).scrollTop();
      
      // whether that's below the form
      if (y+winHeight >= top+ height+gap && y+winHeight<=footerTop) {
        // if so, ad the fixed class
        $('.leftsidebar').addClass('leftsidebarfixed').css('top',winHeight-height-gap +'px');
      } 
	  else if (y+winHeight>footerTop) {
        // if so, ad the fixed class
       $('.leftsidebar').addClass('leftsidebarfixed').css('top',footerTop-height-y-gap+'px');
      } 
	  else 	  
	  {
        // otherwise remove it
        $('.leftsidebar').removeClass('leftsidebarfixed').css('top','0px');
      }
    });
  }  
});

Enjoy fixed floating element or sidebar!!!