Piha Beachstay is a superb place to stay, even if the name is a little misguiding (it's not on the beach, but ~12min walk). The place itself ably caters for couples or dorm groups with large, modern, open plan, airy facilities including TV lounge, dining area, large clean kitchen, terrace overlooking the hills, and more than enough toilets & hot showers. The overall feel of the place is more "friendly log-cabin" than "typical backpackers". Oh, and unlike other NZ places we've stayed in, Piha escapes sandflies, probably as the mozzies have eaten them all. Bring repellent!
A word of advice to those coming to Piha; there's not a lot here in terms of provisioning so you're best to bring groceries with you, topping up day-to-day stuff from the general store 10min away. The Piha RSA club down the road does great steak & chips for $20. Note that most places here take cash or EFTPOS only, so UK guests take note; nearest ATM is 20min drive away... SuperShuttle from airport is $99 1st person + $13 thereafter, private taxi ~$130, I've not tried to get a return yet but I hear there's the Piha Surf Shuttle too for dedicated Auckland-Piha transport.
All in all, I'd come back here at the drop of a hat to spend a few days kicking back, or maybe even taking on the challenging surf. NB people aren't kidding when they say "swim between the flags". According to the cabbie grapevine they've lost 20 people on the W Coast beaches THIS YEAR. That's one a day. You have been warned!