P'unk Avenue
Bottomless is an infinite scroll plugin that has been torture-tested by naive users with old versions of IE, which is important because permanently replacing pagination with infinite scroll on a public facing site is a high risk, high benefit proposition. jquery-bottomless has a sweet and simple API.
When you intend to use a button in your HTML use a button, not a div, span, or anchor. However, if you can't use this plugin.
Walker Crouse
more.js is a small and simple jQuery plugin that makes having a button to fetch additional resources a breeze.