A month or so ago Dan sent me a link to Gliffy.com, an Ajax-y OpenLazslo-driven browser-based collaborative diagramming tool that could conceivably give Visio a run for its money (someday). Even with its limited initial feature set it makes fairly crisp looking diagrams with an intuitive, easy-to-use interface.
Knowledging Across Life’s Curriculum has a brief review of Gliffy, and (of course?) Gliffy has a blog as well.
One thing I have to say is that I hate the product’s logo and its web page looks a bit clunky too. The whole brand presentation would benefit from a makeover by a good designer.