We're renting through
Simes and they've been okay. I would probably stick with Simes, Harcourts, or one of the other larger real estate companies. Also, you can find lots of houses for rent on
Trademe.
Internet and mobile phone providers are up for debate, here. IMHO, it's probably best to try to get at least your home phone and mobile through the same company, and your internet, too. Vodafone and Telecom both have plans that give you favorable rates between their own landlines and mobiles.
As for cars, Chch has about a thousand used car lots. I'm not sure which place will give you the best deal, but I bought mine through
Turners Auctions, with the help of the fellow who owns
AAA Car Rentals. He has good rates on his rentals, too.