I rank hair cuts on three key attributes: how convenient; how cheap; and how consistent. While there is a barber's school down the street from my office that fulfills the first two (but severely lacks the third for obvious reasons), it's Thom's Barber Shop that excels at all three.
Thom's Barber Shop is located on the street level of Ala Moana Shopping Center by Makai Market. With the exception of the last couple weeks before Christmas, parking is usually readily available.
Most of the barbers have been at the shop for years, making it easy find your favorite. Walk-ins are welcome, but I usually make an appointment with my barber to minimize my waiting. The waiting area is a simple bench in the middle of the shop and it can get fairly crowded very quickly.
Men's haircuts are around $11 plus tip, which is reasonable. Be sure to bring cash -- credit cards, unfortunately, are not accepted.