List what you consider the best novels in two separate categories - SF and fantasy - and combined SF/F in the novella, novelette, and short-story length. (Lots of horror in there, too; you pick where you think it best fits.) The 20th century gets 10 ranked positions for each category, and 21st century fiction gets five; I assume this heavier weight-per-year (100 gets 10 slots, 12 gets 5 slots) is because we better remember recent work?
Anyhow, GO DO IT! Here are a ton of resources to refresh your memory (I certainly needed them):
- The Center for the Study of Science Fiction's Basic Science Fiction Library: Mostly lists novels, but also contains some short fiction. This list is ordered by author, spanning all time. Includes publication dates and even links where we could find them! If you see any glaring omissions, please let me know and we'll consult about adding those works.
- The John W. Campbell Memorial Award for best SF novel winners list: Goes back to 1972 novels (that is, the first Campbell Award-winning novel in 1973 was for a novel published in 1972).
- The John W. Campbell Memorial Award finalist list: Goes back to 2003. I recommend looking through the finalist lists of the major awards, because what you might consider the best works don't always win! True for me, anyway.
- Locus put together this fantastic list of 20th century SF/F novels: They mix SF and fantasy, so you'll have to decide on some of these where a novel belongs. How did they get on this list? "The lists include, first, every title that's won a Hugo, Nebula, World Fantasy, Locus, British Fantasy, British SF, Campbell, Sturgeon, Clarke, International Fantasy, Shirley Jackson, or Bram Stoker award [except for first novels categories]. Second, every title that has been a nominee or runner-up for any two of these awards is included. Third, for 20th century novels, every title included in four or more reference works or polls, such as David Pringle's Science Fiction: 100 Best Novels, Neil Barron's Anatomy of Wonder, NPR's recent poll, and some 50 other works and polls compiled as part of the sfadb.com project, is included. For 21st century novels, since relatively few such references are recent enough to cover that period, the bar is lowered to inclusion in any one such work. The bars are set so that the number of titles added to the lists from such references is about the same as the number of titles included due to award standings."
- The Locus list of 21st century SF/F novels: See above notes for details.
- NPR's crowd-sourced Your Picks: Top 100 Science-Fiction, Fantasy Books of all time.
- The Theodore Sturgeon Memorial Award for best short SF: Goes back to 1986 stories of all length shorter than the novel (that is, the first Sturgeon Award-winner in 1987 was for a short work published in 1986).
- The Theodore Sturgeon Memorial Award finalist list: Goes back to 2003.
- The Locus list of 20th century short SF/F. How did they get on this list? "For short fiction, the supplement to awards data is the number of anthology and collection reprints a story has accumulated, based on data compiled in the Locus Index to Science Fiction by William Contento. For 20th century stories, the bar is more than 8; for 21st century stories, the bar is more than 2, though the Index is not complete through 2010 and some recent titles have been added based on manual inspection of various year's-best anthologies. Again, the bars are set so that the final lists are roughly divided between titles via award references and titles via reprint references. For works not on the short fiction lists, there are word-count guidelines on the 20th century short fiction page."
- The Locus list of 21st century short SF/F: See above for details. Also note that the letters in the publication-date info for suggestions of which category to use: ss is for short story, nvt is for novelette, nva is for novella.
- The Nebula Award for best SF/F of the year list: This is Wikipedia's novel list, but also links to all the other lengths. (The official SFWA Nebula Award site only goes back to 2000.)
- Hugo Award for best SF/F of the year list: Links to all the winners, of all lengths, and finalists, too.
Whew, that there's a lot of reading references! I hope you find it useful not just for voting on the Locus survey, but for future reading, too.