Kangaroo Trike - it looked great and read some OK reviews from people using them (see for instance - Musings from a Stonehead). Main problems were cost and the lack of an easy way to get one in Australia with no local importer.
CargoCycle - a Chinese copy of the more familiar (to Europeans anyway) Bakfiets type of bike. I discounted the Bakfiets for similar reasons to the Kangaroo. The CargoCycle looked good but I was concerned the box may not be big enough for my purposes. More recently though I have come across the Gazelle Cabby with an Australian dealer - not sure if they were available in 2007 when I was looking around but might be worth checking out now.
Christiania Trike - From Denmark and it has a local Australian importer, PSBikes. Excellent reviews from my research on the web, very large carrying capacity but with quality comes some cost.
Countdown CargoBike - A cheaper copy of the Christiania.
In the end we decided on the Christiania. Though the 2 wheel versions have advantages in terms of handling (eg leaning into corners) they did not offer the same amount of space to carry the kids up front. We contacted Peter at PSBikes and had a test ride when he was next in our area. Very good service there! As you can see from the photo below my youngest was very keen on the bell!
The ride was a big hit with the boys. For me it took a little getting used to ensure it stayed upright through the corners (a matter of leaning the right way and slowing down until feeling confident). Though not cheap we figured the resale value if we ever out grew it would be very good especially given the comparatively small numbers of these types of bikes in Australia. The build quality looked very impressive with Shimano hub gears, disc brakes up front complete with parking brake built into the handle, 'back pedal' brake in the rear, marine ply used for the box and a host of extras (eg rain covers, kids seats, lockable storage box etc).
To give you some idea of the space up front Peter had one set up for a test ride with two smaller children - thus the car seats are used, safely secured by the seatbelts. In this photo you can also see the handbrake with the red parking lock. So we went ahead and ordered one and Peter delivered it fully assembled in December 2007!