Tokaanu Stream: Heading towards National Park 5k out from Turangi, take a left following the signs. Bring some aluminium foil to cook your fish in the steam barbie. I've been told that the folks in town will sometimes let you use the ones at their motels/resorts for free if you ask nicely.

Taupo: Head out of town on spa road, taking a left when you come to the skatepark. you've gone too far if you get to AC Baths. Park your car (leave nothing valuable) and walk 10min down the path to the first bridge--the pools are in the stream underneath

Kerosene Creek: Take the state highway north from Taupo towards Rotorua. About 40min out of town, you'll see a sign for Kerosene Creek road on your right. Follow the signs to the parking lot, then walk to the waterfall.

There are two in Hawke's Bay:
Tikokino Hut: 4WD across the stream, then walk to the start of the track. There is a warm spring here, but the nicer ones are 1.5hrs up the path to the hut, then another 20min further up hill. Make a night of it.
Ask in the Napier outdoor stores for info on the other--I've never been because of the long hike in.

And of course, Hot Water Beach near Coromandel.

Any other suggestions?

Anybody got any others they'd recommend?