Here are some of the places I have been to and liked in the North Island:

• Cape Reinga - The tip of New Zealand, it is sacred to the Maori, whose spirit travel up here on their way to the afterlife underwater. This is also where the Tasman Sea meet the Pacific Ocean. 
• 90 Mile Beach - The beaches along the west coast have black sand while the east have white sand. The beach is actually only just over half what its name states, at 55 miles. Apparently measuring on horseback weren't the most accurate method back in the days, but the name has stuck.
• Waitangi/Russell - Both towns are historically important, as Russell was the first permanent European settlement and the founding documents of New Zealand, the Treaty of Waitangi, was signed at, well, Waitangi.
• Waipoua Forest - This forest holds the two largest kauri trees in New Zealand, both thousands of years old. Kauri trees are native to New Zealand, is one of the most ancient trees still existing, so there is a great effort to conserve them. Make sure you clean your shoes before and after entering the kauri forests to keep any diseases that may harm them at bay. If you want to learn more about Kauri trees, the Kauri museum in Matakohe is worth a visit.
• Ngawha hot springs - There are hot springs where you pay to enjoy, then there are those that are local secrets and free. This one is probably the cheapest paid hot springs ever (at the time of this blogpost), where a range of water holes offer varying degrees of hotness.
• Bay of Islands - A popular holiday destination for Kiwis, this is the place to go for snapper fishing, skydiving, and dolphin watching.
• Tawharanui regional park - A recent discovery, and a new addition to my favourites list! This area is clean, though popular, with white sandy beaches, camping grounds, walking tracks, cows and sheep and native birds coexisting freely with the visitors. 
• Orewa beach - While Tawharanui is a beautiful spot, Orewa is my favourite 'local' beach becuase it's a lot closer to Auckland. Every chance I get, I would come here for a swim, beach tennis, reading sessions under the shade. I love!
• Muriwai beach - For those who are after a surf, Muriwai is a better bet than Orewa. It's usually quite windy here and can get quite dangerous if not careful. Remember to swim between the flags. You'll see a huge colony gannets, white seabirds with yellow heads. A loves the real fruit ice creams on the way here.
• Piha beach - Another good surf spot but probably a tad more wild, is Piha. There's even a TV series called Piha Rescue following the lifeguards saving swimmers in danger. 
• Raglan - Continuing on with the surf theme, here is a cool beach town all about surfing. Raglan is gaining reputation for its artisanat, as a number of increasingly popular local brands hail from this town, including Raglan coconut yoghurt, Sweet As popcorn, and Soul shoes, to name a few.
• Coromandel and Cathedral Cove - At one of the most pittoresque spots in New Zealand, A fell on one knee to pop the question, I said yes, and we are living happily ever after.
• Waihi - It's pretty quiet around here these days, but it used to be a prosperous gold mining town in its heydays, still in operation today. It also happens to be A's first home in NZ, though it had nothing to do with gold.
• Matamata - Other than the natural beauty, New Zealand is known as the filming location to the Lord of the Rings trilogy and the Hobbit, among others. While they were filmed pretty much everywhere up and down the country, there is an official Hobbiton you can tour around. It's expensive, but is a must for the LOTR fans.
• Rotorua - It smells of rotten eggs here. Blame it on the geothermal activity bubbling away in the hot springs and shooting up geysers. A visit to a (very touristy) Maori village is worth it because it's probably the best place to experience the Maori traditional meal, hangi, cooked underground. Rotorua is also known for its mountain biking trails, and has the tallest commercial fall in the world (7m, grade 5), so if you are after an adventure, make sure you stop by.
• Taupo - The largest lake in New Zealand. Popular activities nearby include Huka Falls, hot springs in the nearby park (free!), and Great Lake Trail.
• Tongariro Crossing - Next to Lake Taupo is Mt Ruapehu, the largest active volcano in New Zealand, within Tongariro National Park. It is home to popular ski fields, and one of the nine Great Walks, the Tongariro Alpine Crossing, and the location of Mount Doom in Lord of the Rings. I loved the 8 hours of Tongariro Crossing and would highly recommend it to all visitors to New Zealand.
• Waitomo glowworm caves - I remember having done this when I was 5 years old. I still remember standing inside a dark wet cave, looking up, as the guide explained the uniqueness of these creatures lighting up the roof like tiny little stars, and carefully stepping into the boat. As a five-year-old I was awestruck. Perhaps you will be, too.
• Napier - Napier is unique for its art deco architecture, built after its 1931 earthquake. It is also known for its wines.
• Wellington - The New Zealand capital city of Wellington is also known as the city of winds. It's hilly, it's windy, but it's also artsy, hip and quirky. Visit Te Papa, the National Museum, tour the Beehive, the New Zealand parliament building, and drink at many of its famous cafes and craft beer spots. I seriously considered moving here before I decided to move to Melbourne instead. Next time I visit, I plan to eat at Pomegranate Kitchen, drink at Havana Bar and shop second hand on Cuba Street.