i know i said harry/ gabbby earilier, but i don't that will work on second thoughts. I guess Harry/Belle would be best. She would be able to balance the light side darkness in her as well. Maybe have her under some parsel-spell or something. Harry is able to break the spell. And then whitelighters can take away the dark mark, and in doing so return her to her 16yrs old state.
an more important question is, when is harry entering hogwarts. if that 11 then belle and tonks stories won't work. they will be too old for him. then i vote for Harry/Fem.Blaise
I hope Harry can enter hogwarts at 5th when he is 16, then having the Belle story line from above will work perfectly (16 old light side grey belle). And you could even have Tonks in the mix as well.
By that time, Dumbles will have changed is target to Neville, so neville will be the golden boy.
Well these are my views and hopes, i hope to see wha you come up with.