Looking for something else entirely, I just stumbled across the Visual Thesaurus Spelling Bee. When I first read about it, I thought that we'd have to spell a word based on a picture of it or something, but in fact the "visual" part gives you a diagram of where the word comes from. Words, spelling and etymology--in game format. It really doesn't get much better than that.
Try the VT Spelling Bee for yourself: http://www.visualthesaurus.com/bee/play . I did have some difficulty with some of the pronunciations (the readers change every few words)--spasmolysis sounded like it had a "t" at the end (although the definitions are given, which should have clued me in). I was pleased to see many of the words Dover spellers have conquered in the past, such as diphtheria and pettifoggery, and mostly I was happy to find a new and very entertaining spelling game. I recommend it.