SpicyNodes is a really cool concept webbing tool. Like most of the other technology resources on this site, it requires registration, but it is free.
Most teachers will agree that concept webs, organizational charts, mind maps, or whatever you prefer to call them, are useful teacher resources in of themselves. SpicyNodes.com takes things one step further though. The same basic premise of linking main ideas applies, but the web-based technology behind Spicy Nodes enables the user to create more engaging, media rich presentations.
Check it out.