Langlock
Incantation: Langlock
Pronunciation: lang-lok
Description: Glues the victim's tongue to the roof of his/her mouth. Created by Severus Snape.
Seen: Used by Harry in HBP on Peeves and on Argus Filch, to general applause.

Legilimency
Incantation: Legilmens.
Pronunciation: le-jil-i-menz (usually nonverbal)
Description: Allows the caster to delve into the mind of the victim, allowing the caster to see the memories, thoughts, and emotions of the victim.
Seen: Used by Snape on Harry during Occlumency lessons in Order of the Phoenix and by Dumbledore on Kreacher. Also used nonverbally by Snape on Harry in Half-Blood Prince to allow him to see where Harry had learned the Sectumsempra spell. Used by Lord Voldemort multiple times to see Harry's thoughts.

Levicorpus
Incantation: Levicorpus
Pronunciation: lev-i-kor-pəs (usually nonverbal)
Description: The victim is dangled upside-down by one of his/her ankles, sometimes accompanied by a flash of white light. Created by Severus Snape. Its counter curse is Liberacorpus.
Seen: Hermione uses it to lift Harry so he can steal the Cup of Helga Hufflepuff. Harry sees (through the Pensieve) his father, James, use the spell against Snape.
Though Harry initially learns Levicorpus as a nonverbal spell, it is used verbally by James Potter in The Order of the Phoenix and by Hermione Granger in The Deathly Hallows.

Liberacorpus
Incantation: Liberacorpus
Pronunciation: lib-ər-ə-kor-pəs (nonverbal)
Description: The counter spell to Levicorpus. Created by Severus Snape.
Seen: Harry uses the spell in HBP to counteract the Levicorpus spell he inadvertently casts on Ron. Harry also casts it on himself in Deathly Hallows after managing to retrieve the Horcrux from the shelf in the Lestrange's vault.

Locomotor
Incantation: Locomotor
Pronunciation: loh-ko-moh-tor
Description: The spell is always used with the name of a target, at which the wand is pointed (e.g. "Locomotor Trunk!"). The spell causes the named object to rise in the air and move around at the will of the caster.
Seen: Parvati Patil and Lavender Brown use this spell to race their pencil cases around the edges of the table. A variation seen in Deathly Hallows is Piertotum Locomotor, which animated the suits of armour in Hogwarts.

Leg-Locker Curse
Incantation: Locomotor Mortis
Pronunciation: loh-ko-moh-tor mor-tis
Description: Locks the legs together, preventing the victim from moving the legs in any fashion. The target can hop when affected by this curse, but walking is impossible without the countercurse
Seen: Used by Draco on Neville Longbottom in Philosopher's Stone. Also mentioned further on in the book as Ron and Hermione prepare to use it on Snape during a Quidditch match. Used by Harry on Draco, who deflects it, in Half-Blood Prince.

Lumos
Incantation: Lumos
Pronunciation: lew-mos
Description: Creates a narrow beam of light that shines from the wand's tip, like a torch.
Seen: First seen in Chamber of Secrets and then constantly throughout the series.
The counter spell, Nox, extinguishes the light while the spell 'Lumos Maximus' enhances it.
The caster of this spell can cast other spells while this spell is in effect