http://www.skritter.com/
There is a free demo but it is recomended that you use a tablet.

I've been using it. It's the best I've found so far for practicing writing. But even with a tablet, it's a little hinky about some strokes. Like the second stroke for mountain... It just doesn't want to take it a lot of the time.

But I definitely think it's working for me. (Writing was by far my worst skill.)

Do you know if it'll accept input from left-handed people correctly? It took me forever to find a 電子辞書 that recognized my left-handed input.

bluemarigolds,
Not only is there a demo for symplifed hanzi, traditional hanzi and kanji, there is a 1-2 free membership thing. Try it yourself and see if it works.