The top of that list is constantly changing based on either recommendations from others, my own reading experiences (usually by the same author) or just stumbling across an unread book (or series) from my own collection.
For example, folks have been recommending George R.R. Martin’s Song of Ice and Fire series for some time. And my recent reading of Kage Baker’s Gods and Pawns moved her Company novels at the top of my list. That’s not to mention the series that used to be high on the to-read-next list like Banks’ Culture novels, Benford’s Galactic Center books, Butcher’s Dresden Files and Bova’s Grand Tour series…and that’s just the authors whose names start with “B”!
Sound off! What science fiction and/or fantasy series are you dying to read?