If you’re sitting in front of a computer right now (very likely) and just want to zoom around New Zealand’s topo maps, you could check out Gavin Harris’s New Zealand Topographic Map  website.
Gavin’s stitched together all of the current Topo50 maps from Land Information New Zealand, into a big giant topo map of New Zealand. It’s now available through a handy zoomable and scrollable web browser interface similar to a simplified Google Maps but instead with good topo maps of New Zealand. It’s very handy for quick reference of what’s in an area without having to pull out big paper maps, and it’s easy to send around links to specific areas on the map. For instance, here’s the area around the Holdsworth/Jumbo Loop  which is one of the most popular weekend tramps in the Tararuas.
Gavin’s website follows the LINZ removal of it’s NZ Topo Online service , which it no longer considered necessary now that it’s providing downloads of all its Topo maps in various static formats.
Update, 30th August: Coincidentally launched at about the same time, there’s now also another very similar service called NZ Topographic Maps  that’s just been made available, by Reuben Williams of Seagull Web Design. The latter service utilises Google Maps, and paints NZ Topographic maps over the top.