Check this out, this designer is free (Open Source with EPL license).
UML Designer which can be used for:
- Package Hierarchy
- Class Diagam
- Component Diagram
- Composite Structure Diagram
- Deployment Diagram
- Use Case Diagram
- Activity Diagram
- State Machine
- Sequence Diagram
- Profile Diagram
Got good tutorial as well:
http://www.umldesigner.org/tutorials/tuto-getting-started.html