Really? You’d pick Rio? I wouldn’t trade my time there for anything (I finished my Master’s degree on a study abroad program in Rio). But there’s no way that’d be the place I’d go for a full year.
I’ll jump on the London bandwagon. I’ve never been there, but I think that would be pretty cool. Easy access to Europe, but no day to day language problems.
Those of you that are guests and those of you who don’t have your real location posted in your profile… I’d be interested to see where you currently live.
For example, Maastricht said “Hawaii” (well actually I think he said “Hawai,” but we all know what he meant), which is more interesting to me because his location is: Dutch in the Netherlands
Philster, you get the award for the best profile Location. That cracked me up.
New York City.
Edmonton, Alberta, Canada.
And I’d work at the West Edmonton Mall.
Canadopers will understand.
And yes–I watch 6teen. 
Lots of family there and a love of the Brazilian culture and Portuguese language.
I’d go with New Zealand. Such a beautiful country, but too far from home to move permanently, so a year would be perfect. I’m on the market for a post-doc - anyone hiring??
Currently living in DC.
Brisbane or Sydney Australia.
I’ve been researching for years…
Ireland
Oh, boy! Ocean City, Maryland for sure!
At the beach year 'round, small town, I can walk if I want to almost anything, and they sell booze at convenience stores. Not too snooty, not too skanky. 
New Zealand for me too.
Kakapos!!!
Somewhere in France. Or Taipei, Taiwan.
Amsterdam
… Brassy I agree about those cheeky green parrots … went to see them at night when I was on Stewart Island …
… Sottish Highlands …
McWoAus
Only one year in Hawaii would kill me. It would have to be for multiple years.
I think for one year, I would either opt for Tokyo or a major European city–probably Paris or Berlin (we have a good friend in Berlin, and it would be rad to be able to live in the same town as her). In either case, I would want an interesting metropolitan base from which I could explore the continent (either Europe or Asia).
My sister and her husband lived in Hawaii for a year, and both agreed that it was just about the right length of time. That was when the downsides of living there began to outweigh the upsides.
Wanna swap lives?
Greenland
Wow, I never would have expected this answer. Do you know what winter is like here? For that matter, do you know what summer is like here? 
I’m going to say London or New York if I had to work. But if I was retiring somewhere, my vote would be for Cuba.
Got a line on a job there?
Semi-serious.