Online diagram tool: Gliffy
I’m a big fan of sketching diagrams on the computer to get to grips with complex ideas and processes - I’ve written before about dia, my favourite desktop diagram tool. Here’s an online tool, Gliffy, that looks like it does a similar job.

You can add shapes and connectors from various different palettes and set colours and other attributes. Impressively, it has export to a number of file formats that mean you could download your diagram and open it in another editor, or put it on a web page. You have to sign up but it’s free, although they do also have a premium account.