Some free software ER diagramming tools

RISE Editor

http://www.risetobloome.com/

UML tool for draw UML diagrams fast (a free software)

Free UML Tool for Fast UML Diagrams

UMLet is an open-source UML tool with a simple user interface: draw UML diagrams fast, export diagrams to eps, pdf, jpg, svg, and clipboard, share diagrams using Eclipse, and create new, custom UML elements.

download : http://www.umlet.com/changes.htm

ArgoUML

http://argouml-downloads.tigris.org/