My number one tool from the Web 2.0 Awards list is Del.icio.us, the social bookmarking site. This application is used for tagging and sharing bookmarks with friends as well as other users. Google Docs makes a close second, providing me with word processing over the internet. This can be used with other users to create projects in real time.
I use PB wiki in one of my classes. I like that it is user friendly.