UMLet

After searching for the best (free) UML tool. I've finally found it! It's called UMLet and can be downloaded here.

UMLet can be downloaded as an Eclipse plugin or standalone application. I currently use it as a plugin within Eclipse. There are no limitations in use, in contrary to other so called "community" editions of payed tools.

It features the following:
- snap to grid of elements
- export formats: PNG, GIF, JPEG, SVG, EPS, PDF, and BMP.
- customizable diagrams
- drag-and-drop interface

UMLet supports a variety of UML diagram types: class diagrams, use case diagrams, sequence diagrams, state diagrams, deployment diagrams, activity diagrams, and custom diagrams.

For screenshots, click here.