The Unified Modeling Language is a neat set of standards for design artifacts. There are books (and books and books) on UML. If you have a good school library, look for Craig Larman (forget the title) or Quatrani's Visual Modeling with
Rose as introductory works. Scott Ambler has a bunch of good books and a highly distilled overview of the various diagrams at
http://www.agilemodeling.com/artifacts/index.htm. What you need to produce is highly dependent on your application and your audience. Drop in to the OO,
Patterns, UML and Refactoring forum if you want to get more dialog going with the gang here.