Once again I'm working on a project and I'm wondering what tools people use for visualisation of their classes?

I can see that Xcode has the class modeller but I believe that is currently read only. Are there other tools out there which will help me generate the class files from the model?

Haven't used one since my Java days, so that won't be helpful. How much design do you do up front before generating code? I've never found that very useful as the code always changes, forcing constant update of the models.