Most of the ones I own I've read numerous times but the first two I always think of to read again (and reading those then starts me reading all the rest ) are Memory Prime and Traitor Winds.
Dark Mirror -- Easily my favorite Star Trek book ever. Crossroad -- probably my favorite TOS novel Home is the Hunter -- brilliant and overlooked character studies on Chekhov, Sulu and Scott Prime Directive -- read at least 4 times, never disappoints Probe -- read this once about 20 years ago and it stuck with me. I need to re-read this one to see if it's as good as I remember.
I agree there, only I would enjoy not being behind on the new novels though. It tough to avoid spoilers for very long, and I would enjoy experiencing the new books along with everyone else when they first come out.
The only Trek fiction books I've read more than once are "Star Trek Logs 1-10", "The Motion Picture" novelization, "The Entropy Effect", "The Wrath of Khan" novelization, "Strangers from the Sky" and "Andor: Paradigm". I've also heard everything that is on audio from Simon & Schuster Audioworks, so it does seem like I've reread quite a few titles sometimes.. One day I really hope to find the time to reread "Final Frontier", "Uhura's Song", "The Romulan Way", "TNG: Metamorphosis", "Ex Machina", "Captain's Table: New Frontier: Once Burned", "New Frontier: Stone and Anvil" and "Typhon Pact: Paths of Disharmony". That's how I found Larry Niven's "Known Space" books, including the kzinti in "Ringworld", DC Fontana's "The Questor Tapes" novelization, David Gerrold's amazing "The Man Who Folded Himself" and his "Dingiliad" trilogy, and Vonda McIntyre's "Dreamsnake and Other Stories".
^This seems an opportune time to mention that my Only Superhuman will be out in paperback in a bit over a month... And of course there's good science fiction out there even by people who haven't written for Star Trek.
I've read Articles a few times as well as the first book of the NF series & Shadows of the Empire. I know the llatter isn't a Trek book but it was one that jumped into my head. Read the Destiny books more than once as well & The Forgotten War by William R. Forstchen. Really like that one.
The Final Reflection is the one I seem to go back to most often. Other ones that I have read multiple times areThe Wounded Sky, My Enemy, My Ally, Strangers From the Sky and Prime Directive. There are certainly newer ones that I would like to reread, but have sadly never made the time: Serpents Among the Ruins, Articles of the Federation, A Stitch in Time, the Destiny Trilogy, Watching The Clock, The Never-Ending Sacrifice... well, the list goes on, really... In non-Trek, probably my most reread is the Hitch-Hiker's Guide to the Galaxy "trilogy". I'm actually sort of in the middle of going through that one again now!
I have never been able to get enough of Serpents Among the Ruins. I have honestly lost count of how many times I've re-read that book. I have re-read Uhura's Song multiple, multiple times. The Vulcan Academy Murders has been re-read at least ten times. I have also re-read, at least three times, Yesterday's Son and Time for Yesterday, The Pandora Principle, The Entropy Effect, and, of course, Federation and Prime Directive. I couldn't possibly list the number of books that I've read at least twice. It's funny that, although I love the modern 24th Century continuity, I can't think of a single book I've re-read more than twice, and even then only a rare few.
I'd say almost anything by either Diane Duane or John Ford. For that matter, while Diane Carey's politics are a bit hard-libertarian for my taste, I rather enjoy her Piper and Robert April/Geordie Kirk books.
There are certain books that I like so much and could re-read over and over again that I purposely DON'T read except for once a year, so that, like fine wine, can be enjoyed and savored and be fresh each time. The first on the list is Voyager: Full Circle by Kirsten Beyer . That book is so touching, yet adventurous at the same time. I was never a big fan of Chakotay but my heart really broke for him in that story and made me not only a fan of Chakotay, but finally accept him as captain of Voyager. Beyer knows these characters, and even better, loves them as well as we do. It shows. She took Voyager from the episodic and brought it into the epic. Full Circle, was like Star Trek Voyager: The Motion Picture. Everyone book following this one was like going to a movie sequel, a treatment the Voyager storyline, desperately needed. I get what someone was saying about Janeway being dead, yet alive in Full Circle. She impacts the narrative and the last scene with Janeway and Torress, where she goes to confront B'eLanna about the holoemitter really made you sad that you knew she was dead, like you would an old friend. The next is Ex Machina by Christopher L. Bennett. TMP was the first STar Trek movie I ever saw and it was in a drive in theater at that! I don't remember the story from that night but what I do remember, which is why I fell in love with Star Trek at such a young age, was that the Enterprise, being huge and breath taking on that massive screen, became my first love. My favorite seen in the novel was in the beginning when Kirk couldn't take his eyes of the refit Enterprise, reminding me how I felt when I first saw it. It was the one thing Kirk and I had in common, our love for the ship. And in ways none of the other Trek captains have seen doing since then. The novel not only takes me back to that time but also is a great sequel to the movie. I could see this book easily being made into a motion picture sequel that made it to film. Plus after TMP focusing so much on Kirk and Spock it was great to see McCoy get some character time. And really good to see the ship and crew in the second DTI novel.