CNN's Business 2.0 magazine has published a list of The Next Net 25. These are the websites they say are reinventing the Web. Bloglines, Newsvine, Last.fm, Technorati and digg - all sites that I use regularly - are mentioned but there are also two or three interesting sites that were completely new to me. One of the sites CNN featured, Writely, was recently acquired by Google - a deal that BusinessWeek followed up with an good overview of Web 2.0.
Another list worth reading is DesignTechnica's guide to The Best of Web 2.0. Again, most of them are fairly well-known but there are a couple that were new to me.