Concept Mapping Online:

DabbleBoard
This is a very user-friendly program. It also has a "Share+Chat" icon that allows you to instantly email yourself (or others) a link that will get you back to the graphic organizer later- just be sure to click the save button before emailing. Because it has a freehand feature, it works great with Smart Boards.  I contacted the company to ask how long maps created in their free version will be available, and the response was "The drawing will be saved indefinitely".

User Guide: http://dabbleboard.com/morehelp

Bubbl.us
This program creates basic webs. Its not very fancy, all the bubble are rectangles, but it keeps the map neat and professional looking.  It also has a feature to share and work collaboratively with others.

Mindomo
The free version only lets you save 7 maps, but you can create as many as you want and save them to your computer (you just can't change them in the future without starting over).

Webspiration
This is by far my favorite "free" graphic organizer creator, however it is created by the folks at Inspiration and they make it very clear that this is only the beta version and at some unknown time in the future there will be a (unknown) charge to use it.

Pre-Made Graphic Organizers:

For a whole list of sites with pre-made graphic organizers visit:
http://www.webenglishteacher.com/graphic.html

Also visit http://freeology.com/graphicorgs/