Infinite Scroll
http://www.infinite-scroll.com/
the jQuery and Wordpress Plugins

jQuery Plugin:
http://www.infinite-scroll.com/infinite-scroll-jquery-plugin/
currently: version 2.0b.110415

Wordpress Plugin:
http://www.infinite-scroll.com/installation/

As of version 2.0, option names have changed. Here is a list:

$('.selector').infinitescroll({
  loading: {
		finished: undefined,
		finishedMsg: "<em>Congratulations, you've reached the end of the internet.</em>",
		img: "http://www.infinite-scroll.com/loading.gif",
		msg: null,
		msgText: "<em>Loading the next set of posts...</em>",
		selector: null,
		speed: 'fast',
		start: undefined
	},
	state: {
		isDuringAjax: false,
		isInvalidPage: false,
		isDestroyed: false,
		isDone: false, // For when it goes all the way through the archive.
		isPaused: false,
		currPage: 1
	},
	callback: undefined,
	debug: false,
	behavior: undefined,
	binder: $(window), // used to cache the selector
	nextSelector: "div.navigation a:first",
	navSelector: "div.navigation",
	contentSelector: null, // rename to pageFragment
	extraScrollPx: 150,
	itemSelector: "div.post",
	animate: false,
	pathParse: undefined,
	dataType: 'html',
	appendCallback: true,
	bufferPx: 40,
	errorCallback: function () { },
	infid: 0, //Instance ID
	pixelsFromNavToBottom: undefined,
	path: undefined
})


In addition, you can pause infinite scroll to stop it from triggering, and later resume it.

$('.selector').infinitescroll('pause')
$('.selector').infinitescroll('resume')