Predictions for Half-Blood Prince - why the "half blood prince" has to be Snape.
The Snape is a Vampire Theory - or at least half-vampire. (No, really.) Written February 2005 (before we knew more about his parents), but still yummy.
Predictions for Deathly Hallows: First part is Horcruxes, then Snape. I am starting to think these are pretty good predictions (though part of it could be wishful thinking).