The correct tag would be are you?
Neither of you is going to the show tonight, are you?
Note that the main part of the sentence is implicitly negative, because of neither, which explains the choice of are you? over aren't you?
Yes, we always use a positive tag question after a negative sentence:
- You shouldn't take this medicine, should you?
But we don't always use a negative tag question after a positive sentence:
1A: [So,] I am impatient, am I?
would be used when you at last meet the chap who's been telling all your workmates that he thinks you're impatient. It's a request for clarification of his view, or even confrontational.
1B: I am impatient, aren't I?
uses the usual tag question, here begrudgingly asking for confirmation (which one hopes will be given in a not-too-unpleasant way) of one's self-assessment.
2A: The class was dismissed, was it?
This can be used in a way showing surprise at hearing the news, or in a challenging way (challenging the decision to dismiss or the statement that it had been dismissed) as in 1A. It could also be an unmarked form, equivalent to 'Can you confirm that the class was dismissed?'
2B: The class was dismissed, wasn't it?
This is not unmarked, but conveys (more than 2A) the questioner's belief that the class probably had been dismissed, or the questioner's view that the class should have been dismissed (emphasis on was).
Best Answer
First, the terminology. Wikipedia deems tacked-on questions other than those mirroring the grammar of the statement (eg ", yes?") to also qualify as tag questions.
Second, what questions can be tagged onto "You must have felt it too"?
Certainly the suggestions given not containing a verb (", correct?" / ", right?" / ", yes?" / ", no?") and recasts (" ... you did, didn't you?") are all quite acceptable.
"haven't you" doesn't work with a single event (an earthquake). It would work here: "There have been several smallish earthquakes this month. You must have felt them too, haven't you?" [", didn't you?" also works here]
"didn't you?" does work here: "I was woken by quite a pronounced tremor last night. You must have felt it too ... didn't you?" [the pause disguises a certain awkwardness resulting from the verb switch]
But "mustn't you" would only be used in a situation like this to persuade someone of what seems inescapable but which they're unsure about, rather than purely to check on facts:
"You must have left it at Auntie Jane's, mustn't you?" [two levels: solicitous or browbeating]
(ie "you've got to agree that it's what actually happened". The 'must' in "You must have felt it too" holds far less conviction; the tag question is proof of that. So ", mustn't you?" is unavailable after "You must have felt it too" here as it defaults to a different sense.)