Hello All. I have an app called "English Idioms Illustrated". It explains the meaning and origin of English Idioms in a comic strip style and the first 30 strips are free.
It's been downloaded a million times and has 596 five star reviews so I think it's a popular and useful resource you might like.
http://itunes.apple.com/us/app/english-idioms-illustrated/id413057971?mt=8