Grapholite is a very slick online Graphic Organizer and Flow Chart creator. The site is very simple to use and has a plethoria of shapes, arrows, tools, colors, and more to customize your organizers any way you want.
The site has a demo mode that allows you to use the tools without signing up or signing in. However, you will need to sign up for an account to save or print your work.
I would recommend Grapholite more for teachers and instructors than to be used by students since you do need to sign up to save your work. However, if you are tired of creating your graphic organizers in Word or Open Office, give Grapholite a look.