Good accents?

I'm British, I think all of them did a great job.

Lets build a snowman!

They were pretty good. Ed Norton and Liev Schrieber were better than Watts whose Aussie twang crept in a few times.

I give my respect to those who have earned it; to everyone else, I'm civil.

Naomi Watts is already English, so her accent was natural but Edward Norton's was a little forced. I'm not English but I'm pretty good at using accents so it was easy to catch Norton's fake accent. Like you said, not horrible, but just not natural.

To me, it was a single facial expression that made Ms. Watts seem Australian, for a moment.

At the party, near the start of the film, Ms. Watts flashed a smile of unbridled derision as she passed one of the guests.

To me, that contemptuous smile was a very Australian facial expression. I have not seen people of other nations put dagers behind a smile in quite that way.

The moment was quickly forgotten. The film and Ms. Watts were spectacular!

I thought they were all good (British accents), but as I'm from the Southeast U.S., I'm most critical of phony Southern accents in films.
One point I noticed, Norton says "eye-ther" [either] and Watts says "ee-ther" in the flower shop and "eye-ther" as she's playing cards with Norton. I wonder why.

I noticed where N. Watts pronounces "either" with a long 'e', then a later scene with a long 'i'.

Was Diana Rigg supposed to have a French accent? I couldn't tell if it was good or not if so.

I came here looking for this thread because the accents really impressed me. This is the movie where non British actors spoke British accents the best in my experience.

Not Renée Zellweger in Bridget Jones, not Maggie Gyllenhaal in The Honourable Woman, no way. But this movie, wow, Liev and Edward did a really good job.