The "Standard American Accent" spoken in the media and generally taught to foriegners is the confusingly named "Midwestern" Accent, which due to internal migration and a subsequent vowel shift, is now mostly spoken in California and the Pacific Northwest.

Interestingly enough, my old Japanese instructor was a native Osakan, who's natural dialect was Kansai-ben; despite this, she conducted the class using the standard, Tokyo Dialect.