The Science Fair Project Guide, from Science Buddies, is a terrific, award winning resource for students and teachers. The site has science fair project ideas, science news, a student section, a teacher and parent section. There are also tips and resources on doing research, how-to's, links to other resources, an ask-an-expert section, and a science careers section.
The site is a great place for students to start when working on science fair projects or even doing other science research.