Books on American Slang, Dialects, Idioms and Accents

I have a friend at my workplace who hails from Ethiopia and speaks English well, but he is interested in learning more about American slang, dialects, etc. I have found several wonderful online resources, but he does not have internet access and asked if there are any books I could suggest.
Does anyone know of any good reading material on any of these subjects? He said even dictionaries (in the case of slang) would suffice, but I was thinking a basic treatment would be best. I found a lot of work on British English but very little on American English.
Thank you!