I notice that many people have gotten curious about the original series after seeing the movie. There are also some quite good novels, many by writers known for original sf/fantasy. Here's a brief, non-comprehensive guide:
The Spirit of WonderDiane Duane did the best job of capturing the joy I felt when watching the series. You want to serve on her Enterprise – and her Enterprise probably has a place for you. Her crew is full of aliens, and her stories are all about the longing to breathe in the air of a strange new world.
Spock’s World intersperses a mission to Vulcan with a series of heartbreaking vignettes from Vulcan’s history; the alternation of the intense emotional content of the historical chapters with the more contained emotions of legal trial in the main story works beautifully.
Spock's World (Star Trek)
In
The Wounded Sky, the main character is a female giant transparent spider physicist, and the story is about the ultimate in exploring strange new worlds, a journey both inward and outward. Poignant and beautiful.
The Wounded Sky
Enterprise: The First Adventure, by Vonda N. McIntyre. An epic of alien contact, featuring nice roles for all the main characters (even Janice Rand, who is mentored by Uhura), plus backstage comedy via an interstellar circus (!) and a very angsty and interesting original Vulcan character. Her new crew realistically fails to mesh, then gradually bonds; her aliens and descriptions of zero-g are lovely.
Star Trek Enterprise The First Adventure
John M. Ford, as always a category unto himself
The Final Reflection might as well be an original sf novel, as most of the characters are Klingons – and much more sophisticated and interesting Klingons than actually appeared on the show. A beautifully written and powerful story about power, politics, identity, and the costs and rewards of the choices we make. I can’t be more specific because I have no idea what was going on for a great deal of the story (let me know if you do!), but that’s true of most of Ford’s novels.
The Final Reflection (Star Trek, No 16)
How Much For Just The Planet? A musical comedy. No, really. No,
really. And it’s actually funny! It’s kind of a parody, but a very fond one. Kirk and the rest end up on a planet in which everyone acts like they’re in some old movie. Uhura lands in a film noir, and Kirk in a chorus line. There are hilarious film strips and an attack milkshake. Oh, just read it.
How Much for Just the Planet? (Star Trek, No 36)
What if the Series Hadn't Been Totally Sexist?
My Enemy, My Ally, by Diane Duane. A Romulan woman commander develops a prickly friendship with Kirk when they’re forced to adventure together for reasons of political intrigue. Lots of convincing detail about Romulan culture.
My Enemy, My Ally
There are sequels that aren't quite as good.
The Entropy Effect, by Vonda N. McIntyre. Time travel, Angsty!Fencing!Sulu, cool alien characters, several cool original female characters, and a rather slashy Kirk/Spock relationship: what’s not to love?
The Entropy Effect (Star Trek)
Uhura’s Song, by Janet Kagan. This is another one that’s almost an original sf novel. When a plague hits, the cure involves going on a quest with a bunch of catlike aliens on their home world. There’s an original female character whom a lot of people call a Mary Sue, but all I can say is that I only wish Mary Sue was usually portrayed as Buckaroo Banzai, Trickster Archetype. Sweet and fun.
Uhura's Song (Star Trek No 21)
Crossroad, by Barbara Hambly. A remarkably dark and often darkly funny story involving Lovecraftian horrors in spaaaaace. Christine Chapel is a major character, and her (non) relationship with Spock is developed convincingly and poignantly.
Crossroad (Star Trek, Book 71)
Not My First Choice, But Worthwhile
Star Trek, Log One, by Alan Dean Foster. Based on the animated series, this is nothing really special but nicely written.
The other novels by Barbara Hambly and Diane Duane are worth reading if you enjoy the series, as are Jean Lorrah’s. I note that Laurence Yep, Peter David, Joe Haldeman and Greg Bear all wrote novels for the original series; I don’t remember them, but they should be at least decent. I vaguely remember enjoying A. C. Crispin’s books.
Run Fast, Run FarAll the novels by Sondra Marshak and Myrna Culbreath are unreadable, though the “Phoenix” ones do have Kirk naked (and tortured) for most of the book. Avoid, even if that’s a selling point.
The Tears of the Singers, by Melinda Snodgrass. Oh God. Uhura meets a tousle-haired, temperamental asshole of a hot genius musician with a heart condition that will kill him if he gets excited. A planet of baby seal aliens are being clubbed to death by Klingons for the jewels they weep at the moment of death, only their song is holding the universe together. Kirk drafts the musician because he’s the only one who can translate the song, and he dies operatically in Uhura’s arms after saving the world. A baby seal alien spontaneously sheds a single perfect tear of woe, which Uhura makes into a necklace.
The Tears of the Singers (Star Trek, No 19)
Did anyone read
Spock, Messiah? Was it as dire as it sounds?
SPOCK, MESSIAH! (Star Trek)