My favourite pairing......Keanu Reeves and Wynona Ryder in Bram Stocker!Wynona was actually quite good 90% of the time but, oh boy, that other 10%. As for Mr Reeves, I just kept expecting him to say "dude" ! It would have been less distracting if they had just spoken in their normal accents, or just a polite version of it.
As for good accents, I agree with those mentioned already but has anyone noticed that Nigel Tuffnell from Spinal Tap was actually born and raised in America ! Mind you being an hereditary peer in the House of Lords might help.
TTFN M'Lady P.