A year ago I tried some UML tools for Eclipse. I don't know if that has changed recently but I didn't find any good open source solution (Modelling tools are always extremely expensive) for WYSIWYG UML with Round Trip engineering (meaning changing your code will change your UML model and vice versa). I found Omondos UML Plugin the best commercial UML Eclipse plugin. There is a trial version, too, but it's probably not a good choice if your project is short on money (a 1 developer licence is around 4000$).
