Don't forget, in the Chamber, the memory of Riddle did not kill anybody, so another horcrux could not have been created at that time. I think he did want to make Gryffindor's sword a horcrux but was unable to get it. We shall see.

The killing of James and Lily could have allowed him to make Harry a horcrux, but I think he was waiting for Harry's death to split his soul for the final time. Thus I think his soul didn't get the final split until the beginning of GOF, at which time Nagini was probably made a horcrux. Dumbledore kinda explains all this and I buy it until otherwise noted.

I'm still on this notion Shim said of Hogwarts as a horcrux. Destroy the school in order to destroy Voldemort. That is just the coolest idea. Much more meaningful for Harry than Gryffindor's sword.