KiwiSaver was launched on 1st July 2007 and is a low fee and subsidised retirement savings scheme available to permanent NZ residents.
You can join up to the age of 65, and your funds are 'locked in' until you reach the age of eligibility for NZ Super, which is currently 65, or for five years, which ever is later (if you join at age 64 - you can't get your funds until age 69.)
There are Government subsidies ($1000 kickstart for every member, up to $521 per annum if you contribute $1043 per annum), and employer contributions (currently 2% of your income before tax, rising to 3% on 1st April 2013.)
Even if you are 'retired' when you return to NZ, it could well be worth you investigating having a KiwiSaver investment for yourself and each of your family members.
You get to select one fund manager (you have total choice) to manage your funds.
Other topics for you to look at if you are returning to live in New Zealand:
By Carey Church