Gliffy is a web-based application for creating flow charts and diagrams. I found this tool very useful in particular for LIS 533: Database Design for Information Management (IT).  I also used it to make an organization chart for LIS 504: Leadership and Management Principles for Library and Information Services.

 

The free basic version allows you to save up to 5 documents when you create an account. You can create UML/ER diagrams, organization charts, Venn diagrams, floor plans, etc. The application allows you to export the diagrams as a jpeg or png file and print to paper or pdf. You can also share and collaborate. A great tool all around!