I often find myself using the open source program UMLET, which is a great, FREE modeling program. However, I needed to add some greek letters to a model, and could not find any, so I rolled my own. They also have an Eclipse plugin, but I have not used it. You should check them out.
To use the Greek letters palette, just download it and unzip it to the palettes sub-folder of the UMLET folder. It should appear when you next run UMLET