Take a look at Merriam-Webster's new Visual Dictionary Online and tell me if you find it useful. Warning: the website requires Java. The title is a bit misleading, because it isn't really a dictionary. You can try to look up words with the Index, but if they aren't already depicted, you won't find a definition or reference. Granted, I'm not this kind of a visual person (I prefer PCs), so I can't effectively evaluate this service. I tried playing along with the Theme arrangement and found entries that appear to be from an elementary school textbook. The selection is quite limited, too. I don't know why Merriam-Webster's name is on it. I'd be ashamed to call it mine.