Web Based Projects is a compilation of web-based projects that were created by student teachers at the University of Richmond. These web-based projects are a great resource for other teachers to use and the site sorts them by grade level and subject area.
There are WebQuests and WebUnits available. A WebQuest is an inquiry-based lesson in which all of the information that the students work with comes from the web.
I found some great projects to use with my students, including one on Bridge design.