I worked with English actor Max Minghella in the ADR studio for the TV version of some of his lines for Art School Confidential, in which he does an American accent.
I coached two American actors into African accents on the set of Without a Trace.
I recently reunited with my old (young) client, Aaron Fors, and we polished his English acccent for Disney's Movie Surfers for the UK and Scandinavian markets.