Dazu fällt mir nur "right?" ein.

I thought of the same thing as Werner. People often use "are they?" in cases like this, but some people consider it a mistake, so it might be worth avoiding in careful writing.

Ich (als Non-Native Speaker) tendiere hier auch am ehesten zu

"... right?"

bzw. umgangssprachlich: "... eh?"

I think few Brits would flinch at "are they?", though. It's the colloquial/idiomatic tag to use and is referred to neutrally in grammar books, as I recall. "right" (still?) has a vaguely AE air, IMO and, if anything, may even get a more disapproving reaction in the UK than "are they?", depending on the situation or listener/reader.

...are they?

I've been teaching this for 40 years. Of course it's not a mistake, it's the only possibility.

Agree escoville.
... are they?

Right? sounds much more casual and very un-British.

People say "right?" all the time in the UK; the effect it has depends on how hesitantly you say it. I've never thought of it as American. I agree that "are they" is also perfectly common in speech, though.

Right? Very contemporary correct American English.
Are they? Correct, agree with others who said that.

Alt: Don't you think? Maybe that's slang American English.

Wie wäre es bei "Nothing is impossible"? Hier würde ich intuitiv "is it?" bevorzugen.
Und bei "Nobody's missing" scheint mir kein question tag zu passen...

#9: Wie wäre es bei "Nothing is impossible"? Hier würde ich intuitiv "is it?" bevorzugen.

That's right.

#9: Und bei "Nobody's missing" scheint mir kein question tag zu passen...

"are they?" is the obvious one for native speakers from the UK (same as for "Nobody's perfect").

There are other points I'd like to make about the other posts but don't have time right now. It's certainly worth looking at good grammar books on this: question tags are a complex topic and probably one of the hardest things about English.

I find "..., right?" can be very irritating. I wouldn't recommend it to a foreigner.

What if the foreigner wants to be irritating? :-o

No foreigner would ever dream of wanting to be irritating, right?

SCNR

This one certainly never does. Honest.

You can't stop your foreigners being irritating if that's what they want to be, but you can warn them against being irritating by accident.

I thought we were irritating simply by virtue of being foreigners. I had no idea I was supposed to be making an effort.

My father used to go ballistic at "Everybody" and Nobody" used with a plural verb or what have you. That aside, I do think "are they" is widely used and accepted as the right question tag. We are speaking in the gramatical singular, but thinking in the plural.

Nobody's perfect init?

If you're from London and really want to irritate the linguistic purists :o)

M-W Dictionary of E. Usage 1995 has quite a long discussion of "they": http://books.google.de/books?id=2yJusP0vrdgC...
Describes it as "common standard use" but also lists various people who complain about it. Hence my warning that some people dislike "they" here. Them* foreigners need to know that too.

*warning: don't use that either!