Rabbits or hares would be great. They're instantly recognizable animals. Practically anyone above a toddler age (and quite a few of those!), with any knowledge of animals, no matter how little, knows what a rabbit is. They don't get a lot of discussion or drops into the various meta lists we've had because they're just not look at as zoo animals. That's not to say that zoos don't have them, many do, but they're part of that group of animals that people just don't think of when they think of zoos. The number of people excited about seeing rabbits at a zoo is probably pretty low. Despite all that, I'd definitely be happy getting one or more
ETA; scratch that part about many zoos having them. I took a look at Zootierlist and they're actually not that commonly kept.