Many thanks for the kind remark.What an excellent forum!
I don't know a great deal about other online idiom dictionaries, but we have one here at UsingEnglish.com! See: http://www.usingenglish.com/reference/idioms/. It's very new and still being developed, but you might be able to find what you're looking for there.
PS - If you have any suggestions for additions to our idiom dictionary, please feel free to post them in our Comments & Suggestions forum.
- For Teachers