Magic of the Battle
The Battle of Hogwarts had many astounding examples of powerful magic. From professors to students to Death Eaters, magical ability was truly put on display during the fight. Some of these examples include:
Protective Magic: The professors and those inside Hogwarts started protecting the castle as soon as they were aware of Lord Voldemort's eminent arrival.
This was some of the most powerful magic to take place that night. One example of this is the us of the spell "piertotum locomotor" used by Professor Mcgonagall. Using this spell she was able to bring the many suits of armor and statues inside Hogwarts to life to defend the castle against Lord Voldemort's forces.
Voice Magic: Throughout the battle Lord Voldemort used a powerful "sonorus" spell to communicate with those fighting within Hogwarts. His first message was before the fighting actually began. He encouraged those inside the castle to hand over Harry Potter or they would be attacked by his Death Eaters. Those inside Hogwarts did not give in to him and the fighting began. After a great deal of fighting had occurred, Lord Voldemort used the spell again to announce a temporary end to the fighting. He requested that Harry Potter hand himself over or he would join the fight this time. He also warned Harry that if he did not come, Lord Voldemort would "punish every last man, woman, and child who has tried to conceal you from me."
Fiendfyre: Vincent Crabbe used this form of magic as an attack on Harry, Ron, and Hermione as they were searching for a horcrux in the castle. It is a powerful dark spell that produces fire in the shape of large flames and eventually in the shape of certain creatures. It is extremely deadly, but very hard to control. The spell ended up backfiring on Crabbe when he was caught in the flames and became a victim of the battle. It did, however, prove useful for the trio as they were able to use it to destroy one of the horcruxes.
Dueling: The Battle of Hogwarts witnessed some incredible duels. One of these happened between Professors McGonagall and Snape early in the battle. Professor Snape was rather taken back when McGonagall started fighting him and he eventually fled the duel and the castle. Other intense duels that took place during the battle include:
Molly Weasley vs. Bellatrix Lestrange (Winner: Molly)
Luna Lovegood, Ginny Weasley, and Hermione Granger vs. Bellatrix Lestrange (unfinished)
George Weasley and Lee Jordan vs. Yaxley (Winners: George and Lee)
Neville Longbottom and Ron Weasley vs. Fenrir Greyback (Winner: Neville and Ron)
Antonin Dolohov vs. Professor Flitwick (Winner: Flitwick)
Percy and Arthur Weasley vs. Pius Thicknesse (Winner: Percy and Arthur)
Professors McGonagall and Slughorn and Kingsley Shacklebolt vs. Lord Voldemort (unfinished)
Bellatrix Lestrange vs. Nymphadora Lupin (Tonks) (Winner: Bellatrix)
Remus Lupin vs. Antonin Dolohov (Winner: Antonin)
Lastly there was the final battle between Harry Potter and Lord Voldemort. It was a very short duel with only two spells being used, one by each participant. Lord Voldemort used "avada kedavra" and Harry used "expelliarmous." This simple disarming spell was enough to fight off the killing curse and destroy Lord Voldemort due to Harry's mastery of the Deathly Hallows.
People in the battle
Fighting for Voldemort
Lord Voldemort
Alecto Carrow
Amycus Carrow
Vincent Crabbe
Gregory Goyle
Pius Thicknesse
Augustus Rookwood
Antonin Dolohov
Travers
Yaxley
Nott
Walden MacNair
Avery
Mulciber
Fenrir Greyback
Bellatrix Lestrange
Rodolphus Lestrange
Thorfinn Rowle
Lucius Malfoy
Narcissa Malfoy
Draco Malfoy
Fighting for Hogwarts
Harry Potter
Ron Weasley
Hermione Granger
Aberforth Dumbledore
Neville Longbottom
Seamus Finnigan
Lavender Brown
Parvati Patil
Padma Patil
Terry Boot
Ernie MacMillan
Anthony Goldstein
Michael Corner
Luna Lovegood
Dean Thomas
Ginny Weasley
Fred Weasley
George Weasley
Lee Jordan
Cho Chang
Minerva McGonagall
Severus Snape
Filius Flitwick
Pomona Sprout
Horace Slughorn
Argus Filch
Kingsley Shacklebolt
Remus Lupin
Nymphadora Tonks
Oliver Wood
Katie Bell
Angelina Johnson
Alicia Spinnet
Bill Weasley
Fleur Weasley
Arthur Weasley
Molly Weasley
Percy Weasley
Rubeus Hagrid
Hannah Abbott
Augusta Longbottom
Sybill Trelawney
Colin Creevey
Charlie Weasley
Members of both Dumbledore's Army and the Order of the Phoenix joined forces during the Battle of Hogwarts to take on the Death Eaters and Lord Voldemort, along with those they had recruited or forced to join them. They were later joined by additional family members of those still fighting as well as lesser known professors of the school. Many other students who were of age (and some who weren't) also stayed behind to fight. Their fate is not as well known as those listed above, but their contributions to the fight were a great help.
Creatures in the Battle
The witches and wizards were not alone in the fight. Many creatures joined both sides and fought alongside the witches and wizards.
Giants: At least two giants were recruited to fight for Lord Voldemort despite the efforts of Albus Dumbledore and Rubeus Hagrid when Lord Voldemort returend. However, the other side also had a half-giant in the form of Grawp fighting on their side.
Acromantula: Over 100 acromantulas joined the side of Lord Voldemort and helped Death Eaters storm the castle at the beginning of the battle.
Werewolves: Both sides had a werewolf fighting for them. Fenrir Greyback was fighting for Lord Voldemort and Remus Lupin on the other side. However, only Greyback used his wolf form during the fight to attack people.
Dementors: Over 100 dementors fought for Lord Voldemort. They came close to catching Harry, Ron, and Hermione at one point during the battle, but were blown back by a patronus charm performed by members of Dumbledore's Army.
Centaurs: Over 50 centaurs joined the fight against Lord Voldemort. They shot arrows at the Death Eaters during the fight. Firenze, Bane, Ronan, and Magorian are known centaurs that joined the fighting.
House-Elves: Over 100 house-elves were led by Kreacher into battle. They attacked the Death Eaters as they dueled with members of the other side.
Peeves: Peeves played a role in the fight as well. He was seen throwing and dropping things on the Death Eaters inside the castle.
Other known creatures: Buckbeak, thestrals, and Fang.