I plan to spend two months in NZ (arrive Auckland; leave Christchurch) and AU (arrive Sydney; leave Perth) next year. I am considering renting a car for both periods. Does anyone have any experience with this or know any good companies? Buses and trains in Australia seem to be just as expensive as renting a car in the US.

I just rented with Ezy car rentals in NZ. They were the cheapest by far. If you're renting during the summer consider picking up in Christchurch for cheaper rates.

Is that 2 months total or 2 months in each place? If your going for more than 1 month in NZ I would suggest just buying a car and then selling it at the end. I found it really easy to do and actually made a profit (We bought it for $600 NZD and sold it for $1000 NZD). Insurance isn't mandatory and the paperwork is simple - you can do it at the post office. There are backpacker car markets in both cities and we sold our car within 2 hours. You should easily find a car for around $1000 - $1500 which is probably about what it would cost to rent a car for that time.

There is the risk that you won't sell it ... but the cars are so cheap that it's not a huge loss. It helps if you have some flexibility and aren't on a really tight time table.

If you're not staying for at least a month it is probably a bit too much hassle (although not unreasonable - I met several people who only owned a car for a few weeks!). Poochy has some good advice - Ezy cars are the cheapest and there are usually discounts for doing the trip in reverse.

Also if I get a car in New Zealand, how easy is it to find parking spaces in the city at hostels and things like that. EZY is pretty cheap. Does Australia have something similar? I will be staying for two months at each location. April and May in New Zealand and June and July in Australia.