Infinite scrolling solution covered in revised episode #114: http://railscasts.com/episodes/114-endless-page-revised

index.js.erb

$('#products').append('<%= j render(@products) %>');
<% if @products.next_page %>
  $('.pagination').replaceWith('<%= j will_paginate(@products) %>');
<% else %>
  $('.pagination').remove();
<% end %>

products.js.coffee

jQuery ->
  if $('.pagination').length
    $(window).scroll ->
      url = $('.pagination .next_page').attr('href')
      if url && $(window).scrollTop() > $(document).height() - $(window).height() - 50
        $('.pagination').text("Fetching more products...")
        $.getScript(url)
    $(window).scroll()