Why do you think Tom Riddle's a horcrux? I saw nothing to indicate that, and I think that contradicts what a horcrux is.
I think it's very interesting that each horcrux was destroyed by a different person, respectively:
1. (I don't think this is a horcrux)
2. Harry
3. Hermione
4. Dumbledore
5. Goyle (or was it Crabb?)
6. Neville
7. Voldemort
8. Ron
As for deaths, how could you forget Dobby? I think that was the most significant in the book (in the number of pages talking about it, and him being buried). Also, Severus Snape, Lupin, Tonks, Voldemort, Nagini, and I'm sure there's more.