I recently got a membership to Atlanta's zoo and have been going there to sketch. There a class at SCAD that has a weekly field trip there, so I just kind of joined the group without being in the class. Here are some of my sketches done there.
Sorry about the crappy quality, but I just have a camera at home, no scanner. They were all done with a ballpoint pen (the cheaper the better). I must admit it can be really hard to draw moving animals, but it's definitely fun.