yUML is a tool that lets you create UML diagrams using only <img> tags. Here's an example:

<!-- This is the Image Tag you'd put in your blog post -->
<img src="http://yuml.me/diagram/class/[Customer]<>-*>[Order]" />

And this outputs the following image.

The useful thing about this is that, if you learn the DSL used to for the img tags, you can create diagrams straight from your blogging tool. This makes it useful for bloggers or analysts who want to embed diagrams in their documents.

To get a feel for what's possible, see the class diagram samples and the use case diagram samples.

yUML also has a simple online editor for those who want to generate a diagram online, and then drag it into Word or LiveWriter, or a folder on their disk.

This product is only in Beta, and I'm hoping it can blossom into something truly useful and valuable. I need to start thinking about how to fund the hosting, and how to speed up the image generation for starters!

I'd be really interested in hearing opinions and feedback from anyone that uses it. Even if it's just "This SUCKS" :)