I just discovered VisuWords, an online graphical dictionary. I'm loving it (but I'm easily swayed by graphical interfaces!).
It not only shows the meaning of words but it also shows relationships between words. And it looks fun too (did I mention that?!)
Have a look and give it a try. Unlike the more sophisticated-looking Visual Thesaurus, it's free. Do you know of any others like it? Write a comment and let us all know...