My girlfriend and I enjoy naming things after food, and also giving themes to certain groups. Our first BP was named Lentil. I give especially "cute" names to the ones people might regard as freighting, like our rescue alligator, or gets lives in a petting zoo and we use for school presentations and the like, his name is Muffin. Other than that we just go for what ever food name seems to fit them.

I prefer actual names, rather than a numbering system, because it makes it really easy to know who we are talking about without having to go and check which animal it is. It makes the whole experience feel a lot more personal, and less like I am manufacturing reptiles.