Web 2.0 at school

www.e-tutor.com/et2/graphing/

Advanced web-based graphing calculator allowing students to enter one or more equations and view them with position/intersection indicators and zooming functionality. 

gliffy.com

Draw and share diagrams on the web.

• Diagramming in your web browser without downloading additional software
• Desktop application feel in a web-based diagramming solution
• Add collaborators to your work and watch it grow
• Link to published Gliffy drawings from your blog or wiki
• Create many types of diagrams such as Flowcharts, UI wireframes, Floor plans, Network diagrams, UML diagrams, or any other simple drawing or diagram 
  

www.lovelycharts.com

Lovely Charts is an online diagramming application, that allows you to create professional looking diagrams of all kinds, such as flowcharts, sitemaps, organisation charts, wireframes, and many more... For free if you register.

You can view a screencast here: http://www.lovelycharts.com/screencast.php