crags that are "officially open" in the Port Hills - Jane Fonda, Lyttelton Rock, Cattlestop, Gibraltar Rock, Transmitter.
Castle Hill is definitely open (given it is 1 hour away from CHCH) but not Castle Rock (the one in the Port Hills).
Most of the Banks Peninsula crags have been receiving increased traffic.
But of course just because a crag is "open" (or "closed") doesn't mean there aren't boulders ready to skank you in the event of an aftershock so use your head.
The climbnz.co.nz website is the best source of info.