My prediction, which to my knowledge no one else has proposed, is that Harry destroys Voldemort's soul but dies in the attempt. Voldemort survives as a body without a soul, like Stanley Crouch Jr. (who the fourth book describes as "worse than dead," which is telling since Dumbledore tells Voldemort in book five that his failure to understand that there are things worse than death is his greatest weakness). Voldemort lacks wisdom and doesn't understand that he can get the immortality he technically wants and still be defeated. It's a kind of Greek dramatic ending for the classics major J.K. Rowling.

It also makes sense of the mind-bending last line of the prophecy about how neither can live if the other survives. Voldemort "survives" as a husk without powers or even consciousness. Harry lays down his life to defeat him. I have spoken!

Krum dies while trying to save Hermio-ninny and accidentally kills Voldemort (with the help of the house-elves led by Dobby). Ron was goggling some Veela at the time and Harry was busy polishing his broomstick. Snape successfully claims to have killed Voldemort and finally becomes the Dark Arts teacher as his reward. Dumbledore wasn't really dead and returns as headmaster to great cheers from the students of Hogwarts. Karkaroff marries Madame Maxime and Hagrid locks himself into his house with 400 gallons of fire-whiskey until the next series.

The ending unfortunately will probably be fairly predictable (although I can't predict which one). One interesting theory I saw was that Harry is actually the last Horcrux (see book 6) and therefore must be destroyed to destroy Voldemort.