Small and foldable makes it tougher, I like these, they are small and light and you can rotate one side for listening with one ear, but they are pricey. Not sure if they fold.... http://www.amazon.com/Sennheiser-HD25-1-II-Closed-Back-Headphones/dp/B000TDZOXG
The thing with headphones is always the same, what you need them for, how you hear, the shape of your head, etc. The ATH-M50 are great, but they are not small and foldable.
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