The entry fee for this well maintained zoo is around 5 QAR per adult. You can see lots of animals from elephants to snakes in clean surroundings. The highlight for me was the chance to feed the indian elephant.
Best to check entry times by phone and also whether it is "family day" or "Women and children only" as these can vary.
While I love to see different species of animals from all over the world, I believe that those animals deserve to roam free in their natural habitat, so I'm generally not a huge fan of zoos. They can serve a positive purpose if done well, though, and if they do things like captive breeding programs and conservation education. While the Doha Zoo is not the best zoo I've seen, it's certainly not the worst. Most of the animals have decent-sized enclosures and seem to be healthy. And it's not often you get to see lions, tigers, leopards, and elephants all for less than US$1.50! The zoo is set to expand to twice the size it is now, and there are plans to include a free-flight aviary, a marine world, and 'jungle adventures.' I'm not sure how they're going to create a jungle in the middle of the Qatari desert; that might be worth coming back to Doha in a couple of years just to see!
In addition to the animals mentioned above, you can also see giraffes, chimpanzees, oryx, flamingoes, zebras, a rhinoceros, lots of baboons, various deer and antelope species, as well as several nocturnal species that are kept in a special dimly-lit area so that you can see them when they're active.
Entrance is only QR 5. Opening hours are 7:30-11:30am and 3:30-8:30pm daily except Friday mornings. Tuesday afternoons are for ladies and children only; Wednesday afternoons are for families only. Opening hours can vary according to season so it's best to call ahead.