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Personally, I like Kotoba!, a free dictionary that is downloaded to your iPhone/iTouch, so you can use it anytime. It's a 62MB download, so if your iPhone/iTouch is full you may not want to get it right away. But if you've got space, it's a fabulous application! The kanji entries even include stroke order animations from KanjiCafe.com.
Combine Kotoba! with the iPhone/iTouch's Handwriting input for Chinese and you have a mobile kanji dictionary that you can draw characters into for searching!
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