here'a a few places that I rode around Oct 2011
Auckland /Woodhill trails
Lake Wanaka and Sticky Forest
Lake Wanaka was probably one of the most scenic rides I've ever done in my life, just stunning.
The marked trails are quite different from the UK. Instead of having dedicated trails to ride, different sections of trail are named and you can link up whichever ones you want to make up your own route.
pic of one of the maps at Whakarewarewa Forest. All the listings down the left hand side are trail names to link up.
I met up with locals just by chance at Taupo and Alexandra and they showed me the best bits, some really good riding over there. Good job at Alexandra as the bike shop there told me to go on the railway route which I found a bit boring. When I returned he pointed to the hillside and said go up there then. A whole network of trails but really hard to link them up with no maps or anything. Fortunately I spotted a local and he took me out for a spin.