You can use Depicter to draw simple online diagrams. Depicter is a web-based vector graphics editor. Store your drawings online, or export them to SVG, PNG, PDF or JPEG. This easy online tool dosen’t require Flash, applets or any other plug-ins, just go to the site Depicter to create simple diagrams online.
It has the option to draw simple online diagrams using Free-hand , Line, Rectangle or Ellipse. You can also change the color and add some text to your diagram.
Check the Depicter @ www.depicter.com