I am not sure if I like the terminology of "Web 2.0". I thought most of the things were pointles AJAX implementations (dont even get me started on the X in AJAX, its bloated! I prefer JSON but I am sure that AJAJ just sounds like you clearing your throat) but here is a great list of all the AJAX (grrr) and Web 2.0 applications:

Complete List of Web 2.0 Products and Services