Edinburgh Zoo is a great zoo with loads of animals. I have had some great days out there is recent years. It has the biggest penguin enclosure in the UK, with underwater view areas and a bridge through the middle of the pool. Each day there is a "penguin parade" where some penguins walk by the public on a designated route through the zoo. The parade is usually at 1pm and its a good chance to get to see these animals within touching distance.
Built on a hill, the zoo is sectioned into different areas (African Plains, Reptile Houses, etc). You can now get a safari up to the top of the hill and the guide will give you some information about the animals which you pass.
There are large grassy areas throughout the zoo, so it is an ideal place to take a picnic, although there are a variety of restaurants and cafes where you can buy food.
There is an adventure play area for children, which also has seating for adults to relax.
There are three indoor houses in the zoo, reptiles, fish and the monkey house. These are good place to go if the weather should be bad, as you can spend a great time watching the monkeys and gorillas swinging past and grroming each other as well as a variety of snakes, frogs and lizards.
If you can, I would recommend that you go to the zoo on a sunny day, as you will see more animals and invariably have a better time when the sun is shining.
The zoo has Gorillas, Polar Bears, tigers and lions, camels, giraffes and monkeys, as well as a huge range of other animals. Kids especially will enjoy the zoo.