I think the finches found in the Galapagos were the examples that started it all.
Well, no, the finches demonstration variation within species and adaptation to environment. Evolution posits a change from one species to another. Despite the change from beak to beak of Darwin's finches, they're still recognizably finches. I think what the author is asking for is an example of something that is clearly in the process of evolutionary change. In other words, show him a reptile that has developed the ear of a mammal.
I must warn you, though, that no example will be good enough for a creationist, just as no hard-core evolutionist is ever going to accept the possibility of special creation.
Personally, I think God created the earth, but that He did it through organic means. Creation can be reconciled with evolution but, once again, you're not going to get the zealots on either side to admit that.
Thanks for contributing. Your case - the Galapagos finches - is so far the only case presented.
Who has a better case ?