We went to Taronga Zoo yesterday (ie Sunday) and had a great time. I'm pretty sure the kids got a lot out of it - there were lots of oohs and aahs and smiles. HJ loved the seal show (every kid in the crowd loved it) and LGR enjoyed the reptiles and snakes. I personally loved the meerkats, mountain goats and chimps.
It's also a pretty good day of exercise - lots of up and down hill walking to keep the legs moving.