Create and Share Diagrams on the Web

Create and share diagrams online at http://www.gliffy.com
Draw and share diagrams in your web browser without downloading any software. Diagram flowcharts, redesign your office or classroom layout, floor plan, technical drawings, network diagrams, and more. Gliffy has two ways to make document sharing easy:

Collaboration enables others to see and edit your work by simply entering their emails.
Publishing creates a read-only image of your diagram that you can embed in a blog or wiki if you like.

There is a free version with ads, but the company is working on a fee-based, ad free version also.