There have been Star Treknovels almost as long as there's been a show. The earliest books to take place in the Star Trek universe were released as early as 1967, and the trend continues right up until the present day. Given the popularity of the IP, there might be a new novel every day, and that's not including all the fan fiction.
Given the breadth of choices when it comes to Star Trek novels, it's tough to choose only a few that could be the best. The following choices aren't novelizations of movies or shows, but unique stories that don't appear in other mediums. They do include settings or characters that have already been featured on the big and small screen even though most of them are considered non-canon.
7 Imzadi, By Peter David (1992)
The Next Generation fans will recognize Imzadi as a Betazoid term of endearment. Riker's mission to Betazed early in his career is alluded to on the show several times, but it was never really explored in detail like it is in this book. It's primarily an adventure, that involves time travel and the nature of the human soul.
The term "Imzadi" doesn't mean something casual like "honey" or even a more poetic term like "beloved." It's a deeply spiritual expression about the first being to touch your soul. Not to give away any spoilers, but the lesson here isn't one of universal diplomacy or stunning modern technology, just the ancient knowledge that love conquers all.
6 A Stitch In Time, By Andrew Robinson (2000)
Elim Garak is a familiar name to those who know their Star Trek lore, in particular Deep Space Nine. The character has an interesting history; he was intended as a one-off, but viewers and scriptwriters like the character so much that they wrote him in as a recurring plot device instead. In a further twist, the actor that portrayed the character also wrote this book, and since this novel evolved from a series of diary entries that were part of the show, that makes a lot of sense.
Robinson wrote these diary entries, which go back to Garak's childhood and early training, to explore the character for his purposes as an actor. Another Star Trek and sci-fi writer, David R. George III, heard Robinson read part of the diary at a convention and thought it would make a good novel. The rest might not be canon, but it is history.
5 Rihannsu: The Bloodwing Voyages, By Diane Duane & Peter Morwood (2006)
This is a series of four shorter novels, which can be read separately, but this is an anthology that collects all four under one title. One edition was called Star Trek: Rihannsu but this was a version limited to certain book club members, so those looking for the title in modern bookstores are advised to look under Rihannsu: The Bloodwing Voyages.
The word "Rhannsu" is a word that means "Romulan" and the books follow a small group of characters while giving exposition on the lore in general. For viewers that are interested in Romulan lore, this novel is highly recommended reading, and for those who aren't, these books might change your mind about one of Star Trek's most notorious races.
4 Prime Directive, By Judith & Garfield Reeves-Stevens (1990)
Prime Directive is a novel of what could have been a typical The Original Series episode and features the classic team of Kirk, Spock, and McCoy. Instead of being flippant about the most important rule in Starfleet that nobody follows, this one takes it seriously and gives the reader some real-world consequences as to what happens when it's overlooked.
The plot revolves around an incident in which the crew decides to violate the Prime Directive, and the consequences are disastrous on a planetary scale. Spock helps the crew redeem themselves, however, and uncovers a much bigger plot and enemy in the process. The novel has some prescient ideas, like the beings that call themselves the One, who sound suspiciously like the Borg.
3 The Entropy Effect, By Vonda N. McIntyre (1981)
It's not just one of the oldest and best stories that focus on everyone's favorite Vulcan, it's the first original story in what would become an extensive library of Star Trek novels from Pocket Books publishing. Writer Vonda N. McIntyre was also a biologist, making The Entropy Effect higher on the reading list for those with an appreciation for the science fiction side of Star Trek.
The story revolves around two parallel stories that intertwine; one about Spock and his study of a naked singularity and the other about the transport of a dangerous criminal. The singularity, which is similar to a phenomenon like a black hole, was also the subject of study for the prisoner, Dr. Georges Mordreaux. The doctor, convicted of murder and other grisly crimes, is also a source of fascination for Spock, and as the story unfolds he has to confront and defeat a person he admires.
2 Dead Endless, By Dave Galanter (2019)
Dead Endless is one of the more recent additions to the Star Trek reading library, and it's based on one of the more recently released shows, Discovery. The story revolves around characters Hugh Culber and Paul Stamets, the latter of which uses his mind and consciousness to navigate the secret spore drive.
The story explores the idea of the existence of human consciousness within the mycelial network, and it's not official canon it could fit into the Discovery timeline. For readers who are looking for more Discovery novels, Gallery Books has several others that take place in the same setting.
1 The Eugenics Wars: The Rise And Fall Of Khan Noonien Singh (2001)
This isn't a novelization of The Wrath of Khan movie but one novel in a larger series about the Eugenics Wars overall, and this volume focuses on the rise of Star Trek's most infamous villain. Considering that the movie came out in 1982, and the popularity of the character, it's amazing that it took so long to release a novelization of the same era.
The novel traces the very beginning of the eugenics projects that would eventually give rise to genetically augmented humans and begins on Earth in 1974. The Watchers have a team on earth who have been keeping an eye on the Chrysalis Project; Gary Seven, his human secretary Roberta Lincoln, and the shapeshifter Isis. These characters also appeared on the TOS episode "Assignment Earth" which was intended to be a backdoor pilot for a show featuring Gary Seven.