This is from last year but if you want a very quick, thorough understanding of the most popular, lucrative web apps or Web 2.0…click to find out more. They are organized in their respective genres. Maybe you will find some you are not overly familiar with.
One web app that they failed to list is Stumbleupon. This is a recent find of mine and I thoroughly love it. It finds websites and information I want to read at the click of a button. 😀 It helped me find fun calculators, articles, guides on things I love 😀