Im sure that wildlife purists would say that photos taken at a Zoo don't really cound as "true" wildlife photography. There is something about having all the animals placed there in front of you that makes it seem a bit like cheating. The thing is though that the Zoo is a fantastic opportunity for photographers to practice their craft. The trick is to try and find interesting light, that will turn your photos from just snaps into a really interesting image. The little spider monkey in the image above is my favorite from my day out at London zoo, catching the little guy hiding in the leaves ended up with a wonderful final image.
I spent about an hour in the butterfly and moth enclosure, I recently purchased a macro lens and photographing the butterflies on the leaves resulting in some amazing pictures. I realise now how much more practice I need though, focussing on such a small subject is a tough thing to do!