Fix That Ish - A plugin for fixing things (one thing in particular) in the browser window. No support for IE8 and below.

sgFixThatIsh.js

/*
 * jQuery sgFixThatIsh v0.1 :)
 * http://seangaffney.cc
 * Copyright 2012, Sean Gaffney
 */
(function( $ ){
    
  var opts = { bottomPadding: 8 };
  var $header, $content, $win;
  var contWidth, currentContWidth, headHeight, headWidth,
      footHeight, viewHeight, viewWidth, docHeight;

  var methods = {
     init : function( options ) {

       return this.each(function(){
           
         $header = $(this),
         $content = $('#content'),
         $win = $(window);
           
         contWidth  = $('body > .container').width(),
         headHeight = $header.outerHeight(true),
         headWidth  = $header.outerWidth(true),
         footHeight = $('footer').outerHeight(true),
         viewHeight = $win.height(),
         viewWidth  = $win.width(),
         docHeight  = $(document).height();
           
         $win.bind('resize.fixthatish', function(event) {
           currentContWidth = $('body > .container').width(),
           headHeight = $header.outerHeight(true),
           headWidth  = $header.outerWidth(true),
           viewHeight = $win.height(),
           viewWidth  = $win.width();
             
           if ( (currentContWidth != contWidth) && (currentContWidth >= 768) ) {
             $header.sgFixThatIsh();
             contWidth = currentContWidth;
             $win.scroll();
           } else if (($header.data('fixthatish') == true) && currentContWidth < 768) {
             $header.sgFixThatIsh('unfix');
           }
             
           if ( ($header.data('fixthatish') == true) && headHeight > viewHeight ) {
             $header.sgFixThatIsh('unfix');
           } else if ( ($header.data('fixthatish') == false) && headHeight < viewHeight && currentContWidth >= 768 ) {
             $header.sgFixThatIsh();
             $win.scroll();
           }
           
         });
           
         if ( headHeight < viewHeight && viewWidth >= 768 ) {
             
           $win.bind('scroll.fixthatish', function(event) {
             if ( $win.scrollTop() > docHeight - (headHeight + footHeight + opts.bottomPadding) ) {
               $header.css({
                 'position': 'absolute',
                 'left': 0,
                 'top': docHeight - ( headHeight + footHeight + opts.bottomPadding )
               });
             } else {
               $header.css({
                 'position': 'fixed',
                 'top': 'auto',
                 'left': 'auto',
                 'display': 'block',
                 'float': 'none'
               });
             }
             $content.css({
               'position': 'relative',
               'left': headWidth
             });
           });
             
           $header.data('fixthatish', true);
         } else {
           $header.data('fixthatish', false);
         }
           
       });
     },
     unfix : function( ) {
       $win.unbind('scroll.fixthatish');
       $header.css({
         'position': '',
         'top': '',
         'left': '',
         'display': '',
         'float': ''

       });
       $content.css({
         'position': '',
         'left': ''
       });
         
       $header.data('fixthatish', false);
     },
     destroy : function( ) {
       return this.each(function(){
         $header.sgFixThatIsh('unfix');
         $win.unbind('.fixthatish');
         $header.removeData('fixthatish');
       });
     }
  };

  $.fn.sgFixThatIsh = function( method ) {
    if((!jQuery.browser.msie) || (jQuery.browser.msie && jQuery.browser.version.substring(0, 1) >= 9)){
      if ( methods[method] ) {
        return methods[method].apply( this, Array.prototype.slice.call( arguments, 1 ));
      } else if ( typeof method === 'object' || ! method ) {
        return methods.init.apply( this, arguments );
      } else {
        $.error( 'Method ' +  method + ' does not exist on jQuery.sgFixThatIsh' );
      }
    }
  
  };

})( jQuery );