pjax loads HTML from your server into the current page without a full reload. It's ajax with real permalinks, page titles, and a working back button that fully degrades.

Uses HTML5 push/replaceState. supports IE6/7 too.

A lot of this document is focused on how AJAX applications are making use of the fragment identifier.

"Really Simple History is a lightweight JavaScript library for the management of bookmarking and browser history in Ajax/DHTML applications. RSH serializes application data in an internal JavaScript cache so that bookmarks and the back button can be used to return your application to an earlier state."

CSSHttpRequest (CHR) is a method for cross-domain AJAX using CSS for transport.

Hijax: Progressive Enhancement with Ajax

Hosted JavaScript libraries - clever. If widely accepted would help to reduce page load times for sites that use these popular libraries and would hopefully increase security/stability.

Cometd is a scalable HTTP-based event routing bus that uses a push technology pattern known as Comet.

lots of examples, documentation seems good and there's a bit on PHP+YUI too.

can't say I find the demo that helpful and the scaling issues concern me... never the less, I enjoying stockpiling research.

"With the AJAX Feed API, you can download any public Atom or RSS feed using only JavaScript, so you can easily mash up feeds with your content and other APIs like the Google Maps API."

Basically, how-to mimic autosave for them web.

Poorly coded Ajax is no better than Flash and apparently MS went out to lunch during the rash of "please don't be stupid with AJAX" articles. Breaking the core functionality of the back button is, to quote Buffy, all kinds of scary bad.