American Accent Training is the best book I've ever found...
This is the link to buy it in Korea. It's also available on Amazon.
YES24 - [±¹³»µµ¼*]AAT American Accent Training
It also addresses a problem that Koreans have with the intonation of English.
Korean intonation is relatively flat while English has a lot of inflections and vowels sounds that are held for much longer periods of time than Korean vowels.
I can't recommend American Accent Training highly enough.