The LEGO City Zoo set would feature 2 Zebras, made from the current Horse mold, 2 Monkeys, updated with new printing from the old molds, an Elephant, also with updated printing, and a Polar Bear. With this selection of animals, we get 2 new animals, and 2 updated ones without having to use any new molds.
However, if new molds are a possibility, the set could possibly include a Lion, Tiger, Rhinoceros, or Giraffe.
For other angled photos of the above 3 prototypes, please see my Lego Zoo Flickr Set
Update: 6th April 2013 - More pics of the Aquarium posted on Flickr.
Update: 20th May 2013 - Added Gorilla Island section
Update: 22nd Aug 2013 - Added Butterfly House prototype