In my case, it would be The Left Hand of Darkness - which I have read five times.  It was required reading in three different classes I took in college.

Next would be Fahrenheit 451 and The Time Machine - each of which I have read four times.

How about you? 

I've read Friday by Robert Heinlein once a year for the last 6 years.

Xenogenesis by Octavia E Butler 3 times.

Most of Anne McCaffrey at least twice.

Honor Harington series at least 3 times

Bujold's Miles Vorksigan series at least 5 times

I've read Dune and Stranger in a Strange Land three times apiece and I'm gearing up to do it again, this time adding all the Brian Herbert prequels to the mix.  I read A Scanner Darkly four times in a row when I first got it.

eta: If it counts as scifi, I've read A Clockwork Orange about a dozen times.

Short stories: Clifford Simak's DESERTION; Guy Endore's MEN OF IRON (well worth seeking out); everything by Cordwainer Smith.

Also Sherri Tepper's GRASS.

Last Edited on: 7/10/08 8:21 PM ET - Total times edited: 3

You have picked some very good books  I love the Miles Vorkosigan series. i've read The Warrior's Apprentice 3x.

And   A Stranger in a Strange Land, I cried when I read it the first time.  The second time, I still cried just not as hard and as long :)        

I re-read ALOT, if i enjoyed a book the first time I'll enjoy it again a few years down the road.  And some books have things to say that bear repeating every so often.  Also sometimes it's more relaxing to revisit an old friend  when i'm too tired to take on anything more challenging.    Some of the books that are permanent residents of my shelves are:

any and all  Heinlein-especially Starship Troopers, the Lazarus Long books, Stranger in A Strange Land, and I Will Fear No Evil 

The Darkover series by M Z Bradley

McCaffrey's Pern books and the Freedom series

Asimov's Robot novels and the Foundation series

Sheri s. Tepper- (trilogy) Grass, Raising the Stones, and Sideshow, and The Gate to Women's Country, and The Family Tree

John Varley- (trilogy) Titan, Wizard, Demon

Hitchhiker series by Douglas Adams

(Can't imagine anybody reading the Lord of the Rings only once.  I re-read it every few years and always find something new.  (Christopher Lee says he rereads it every year!))

I love to re-read. My most often read book is not SF but fantasy - I've read "Lord of the Rings" eight or nine times. Sheri Tepper's "Raising the Stones" and "The Family Tree" probably four or five times each. All the Miles Vorkosigan books at least three times, some of them more than that - "Memory" is my favorite among them. Bujold's fantasy "The Curse of Chalion" about four or five times. Vernor Vinge "A Fire Upon the Deep",  Orson Scott Card's "Ender's Game", Frank Herbert "Dune", Larry Niven "Ringworld" all of them at least 3 times.  Fantasy again - Barbara Hambly's Darwath trilogy and Ursula LeGuin's Earthsea trilogy - the other two Earthsea novels not really comfort reads for me; and the Narnia stories. And by now (since I read a LOT, I am fortunate enough to read very fast, and I'm unfortunate enough to have a terrible memory) I've read the first Harry Potter about six times, the second one five times, the third one four... you get the picture.

Number 1 on my re-reading habits is Lucifer's Hammer by Niven and Pournelle. I think I'm on my 4th or 5th copy, I keep wearing them out. And every single one has been signed by Larry!

Running a close second is The Stand, by King. Some people consider it SF, some say it's horror, and some insist it's fantasy. I don't care - the book rocks :-) I'm only on my 2nd copy.

I just wanted to drop in a clarification on the question.  I meant "sf" to be speculative fiction - that includes science fiction, fantasy, horror, and alternate history.  Anything in which events beyond the type which have occurred in the known universe, do occur.  I know paperbackswap has divided the genre up into three forums (science fiction, fantasy, and horror), and that probably serves to separate the exclusively elf-and-wizard types from the exclusively space-fleet types, but for purposes of this question, let's consider all these to share a speculative nature.

And the opposite of "speculative fiction" is "mundane fiction"  ;)  Actually, there's a few pieces of mundane fiction on my re-read list too.

-Tom Hl. 

PS - here's a more extended list of my sf re-reads...

Five times - The Left Hand of Darkness

Four times -Fahrenheit 451, The Time Machine

Three times - Downbelow Station, Dune, A Canticle for Liebowitz, World of Ptavvs, 20000 Leagues Under the Sea, War of the Worlds. 

Two times - there's about a fifty books in this category.

I think I reread less than some of you.  A lot of the books on my list seem to be a classics, propelled with an extra read or two for a class - except World of Ptavvs.  That one's a good book, but I can't figure out why I read it three times.  Maybe I'll have to read it again...

The Mote in God's Eye by Larry Niven and Jerry Pournelle. Certainly one of the best first contact stories ever written, and Pournelle's Co-Dominium universe was very cool. Fyunch-Click!

i81.photobucket.com/albums/j219/Kosmosflot/Pournelle/MoteinGodsEyepaperbackcover.jpg

I don't have exact counts on the number of rereads but I know which ones I've reread multiple times:

The Left Hand of Darkness - probably three times, maybe four. I really love this one.

The Pride of Chanur - several times

Growing up Weightless  - by John M. Ford (3 or 4 times)

Rimrunner, Merchanter's Luck, Heavy Time, Tripoint, Finity's End, Downbelow Station , Hammerfall - by Cherryh (2 and some of them 3 times)

The Legacy of Heorot  - by Niven, Barnes, and Pournelle (At least 4 times)

The Color of Distance - by Amy Thomson (three times or more)

Assassin's Apprentice - by Hobb (three times)

The Warrior's Apprentice - by Bujold (3) I need to get the rest of these to reread.

Islandia - by Austin Tappan Wright (At least 4 times, maybe more)

Most of the Liaden books  - by Steve Miller and Sharon Lee, at least twice.

Watchtower, the Dancers of Arun and The Northern Girl - by Elizabeth Lynn (3 or 4 times)

And last but definitely not least...Heinlein's Citizen of the Galaxy which informed my childhood.

It was fun going through my reading list and picking these out. some of these I love so much that just seeing their titles makes me want to go get them and start reading again....

Twice -

1. American Gods, by Neil Gaiman
2. Dancers at the End of Time, by Michael Moorcock
3. Godmother Night, by Rachel Pollack
4. Skin, by Kathe Koja
5. Perdido Street Station, by China Mieville
6. The Dead Zone, by Stephen King
7. Fahrenheit 451, by Ray Bradbury
8. Warchild, by Karin Lowachee

Three times -

1. The Time Machine, by H. G. Wells
2. Way Station, by Clifford D. Simak
3. Cagebird, by Karin Lowachee

Four times -

1. The Lathe of Heaven, by Ursula LeGuin

Philip K. Dick's Ubik has got to be one of the best novels I've read in a long time.

I've only read it once so far, but it was so good I read it from cover to cover.  I even tried to take a break and sleep and instead ended up waking a few hours later to finish it.  I'm pretty sure I'll end up reading it at least a dozen times or until the copy I have falls apart, whichever comes first.

Either Isaac Asimov's Foundation trilogy or Orson Scott Card's Ender's Game, four and five times, I can't remember which is which ;-).  Both are EXCELLENT!!

Well, as a kid I reread the Star Wars novelizations at least three times per year!  (That would be the Original Trilogy, natch, of course back then it was just known as The Trilogy!)  So that would be Star Wars at least 30, Empire say 21, Jedi about 12...

4 Times: Tolkien's Lord of the Rings (but The Hobbit only 2x for some reason)

3 Times: Herbert's Dune (just the first one, I intend to get around to the rest some day)

2 Times: Asimov's Robot/ Galactic Empire/ Foundation series, Clarke's A Space Odyssey series, Card's Tales of Alvin Maker, Stephen King's Eyes of the Dragon, Wies & Hickman's Dragonlance Chronicles & Legends trilogies

I've currently started rereading Jordan's Wheel of Time series, hoping to finiish by the time book 12 comes out in Fall of 2009!  (I know... good luck!)

The Genesis Machine by James P. Hogan is like crack for hard sci-fi freaks. It's Heinlein-meets-Niven. Great people thing happening around a "suspension of belief " hard sci-fi concept. I've read it perhaps a dozen times over the last 15 years or so.

I've read Adams' Hitchhiker's Guide series more times than is probably healthy.

Oh my, where do you start?

Tolkien's Lord of the Rings / Hobbit. My future husband was given them to read before I seriously dated him! 25 years later, must have been a good test.

Mercedes Lackey Valdemar series

Heinlein...any, all, repeatedly

Eddings Belgariad and Mallorean series

I read very fast, so I read mostly series. It is like meeting a comfortable friend when re-reading some of these books.

i keep a lot of my favorite sf&f books for re-reading.  i'm not sure about which i've re-read the most often - probably the Chronicles of Narnia series since i've had the same boxed set for about the last 30 years.  probably the top two most often re-read series' for the last few years are Laurell K. Hamilton's Anita Blake series (i like to re-read the prior book at a minimum before the new one comes out, and every few years read the whole series again), and the Valdemar series by Mercedes Lackey.  i discovered those in about 1995 and re-read them every couple of years.  the first time i read them all in published order, but when i re-read i usually do it in chronological order - which is also the way they're shelved.

also authors i go back to for old favorites: Robert Heinlein, Orson Scott Card, and Anne McCaffrey.

DH re-reads The Deed of Paksennarion by Elizabeth Moon (the omnibus of the trilogy) at least once a year, along with half a dozen other favorites - mostly Heinlein.

ETA: i was just reading another thread, and i can't believe i left these off!  i *love* the Liaden Universe books by Sharon Lee & Steve Miller.  they haven't been re-read as often as some others yet simply because i found them later, but they're getting there.

I am sure it must be Have Space Suit - Will Travel by Robert Heinlein.  I've read most of his books multiple times, but that one in particular was my favorite since about age 8. 

Lord of the Rings, The Hobbit, and "Hitchhikers Guide to the Galaxy".

When I was younger I also reads alot of Piers Anthony over and over.

Ender's Game: Songmaster & Treason - Card

Neuromancer - Gibson

The Peace War - Venor Vinge

The Snow Queen (trilogy) - Joan D. Vinge

The Moon is a Harsh Mistress - Heinlein

Lucifer's Hammer - Larry Niven, Jerry Pournelle

I re-read The Doomsday Book by Connie Willis about once a year, usually around Christmastime, which is when it's set.  It is not a happy book, but I love it anyway.  I also have a penchant for The Rolling Stones by Heinlein, and LOTR and the Harry Potter series, as well as the core books of Anne McCaffrey's Dragonrider series (some of the later stuff, not so much).