The Harry Potter series boasts a litany of spells over the course of the books, as the wizarding world has thought up spells for nearly every use or occasion. There are some that are used in battle scenarios, healing spells, and even spells that are specifically for day-to-day tasks and chores. Of course, the sheer volume of spells available for use means that it was inevitable that there were a few that didn't make their way into the film adaptations.
In general, as adaptations are wont to do, the Harry Potter movies leave out a lot of details from the books. For the most part, they're not usually vital pieces of information, merely smaller details that add to the characters or world building. The movies didn't have the time to go through every spell that the books featured, which means they left out a few of the more fun, quirky, or impractical ones.
Bat Bogey Hex
This is one of the more well-known minor spells amongst fans, as it was Ginny Weasley's signature hex, which she would often use against adversaries. The Bat Bogey Hex, as one might glean from the name, transforms the victim's bogeys into bats that hang from their nose. This would have been one of the more fun spells to get to see represented on screen, so it's a shame that it didn't make the cut.
Glisseo
The spell "glisseo" can turn any staircase into a smooth surface, not unlike a slide. This charm is mostly used as a protection in the dorms, preventing students from going into dorms of the opposite gender (such as when Ron attempts to climb the stairs to the girls' dormitory in The Order of the Phoenix). This spell was also used later on by Hermione during the Battle of Hogwarts, when she cast it to allow herself, Harry, and Ron to get away from a group of Death Eaters that were chasing them.
Waddiwasi
This spell, also called the Projectile Jinx, can send a small object through the air at a high speed, and is introduced during one of Professor Lupin Defence Against The Dark Arts classes. Lupin catches Peeves the ghost attempting to prank Filch by shoving a wad of gum into the keyhole of the broom closet, and shows his students how to use Waddiwasi by casting it and sending the wad of gum up Peeves' nose instead. It's a fun little moment that hints towards Lupin's mischievous past with the Marauders, but ultimately, it unfortunately wasn't important enough to the plot to make it into the films.
Impervius
Impervius is a spell that gets a fair bit of use in the books but wasn't big enough to feature in the adaptations. Using Impervius on an object basically makes that object repel water, and is mostly used in the series during Quidditch games on the players' goggles or glasses to repel water when it's raining really heavily. Hermione is actually the first one to use it on Harry during an early Quidditch game of his so that he could find the Snitch.
Anapneo
Another potentially useful charm, this spell is used to clear objects from the throat, in the event of choking. The only time it's seen in the series is when Slughorn uses it to get a piece of pheasant out of Marcus Belby's esophagus. It may not have been super important to the story overall, but it would have been a neat detail to build out the world a little more if they had decided to include it in the films.
Permanent Sticking Charm
The name of this spell is pretty self-explanatory, but it essentially just allows the caster to stick an object to a surface for an indefinite amount of time. It's seen in The Order of the Phoenix when Sirius Black explains to Harry that his mother's portrait is stuck to the wall of 12 Grimmauld Place, which is why they can't take it down even when it screams at them. Though it seems like it might have been helpful in a number of situations, the spell itself is never touched on in the movies.
The Fernunculus Curse
On a slightly grosser note, this spell will cause the victim to break out in painful boils if they are hit with it, and is actually used multiple times throughout the books. Harry casts it twice, once in an attempt to hit Draco Malfoy (but getting Goyle instead), and the second time against Crabbe. Hermione also uses a version of the curse to expose Marietta Edgecombe as the one who snitched to Umbridge about Dumbledore's Army in The Order of the Phoenix. Perhaps it was for the best, visually, that this spell didn't get represented on screen.
Densaugeo
However, one spell that would have been very visually fun to see is Densaugeo, which causes the victim's teeth to elongate. Hermione gets hit with this one in The Goblet of Fire after she is caught in the crossfire of a duel between Harry and Draco. It was doubly unfortunate for her because she was made fun of for having large teeth in the first place, and this specific spell certainly didn't help that insecurity.