Dungeons & Dragons 5e
(Player’s Handbook p.108) Warlocks bound to an archfey are able to charm or frighten creatures close at hand and can misty step away and turn invisible as a reaction after taking damage. These warlocks are immune to being charmed and can attempt to countercharm anyone who tries to charm them as a reaction. They can also convince a creature that the creature has been sent into a misty otherworld. In other words, typical fey mischief.
(Xanathar’s Guide to Everything p.54) The Celestial warlock’s patron is a being of the Upper Planes. Want your patron to be a unicorn? Then this is the Dungeons & Dragons 5th edition warlock for you. They get extra cantrips in the form of light and sacred flame, they have a special pool of healing apart from spells, they are resistant to radiant damage, and they deal extra damage when dealing radiant or fire damage. In addition, these warlocks gain temporary hit points after rests and can give other creatures temporary hit points as well, and when making a death saving throw can instead choose to regain half their hit points and deal blinding radiant damage to nearby enemies.
(Tasha’s Cauldron of Everything p.72) Fathomless warlocks have found a force from the depths of the ocean to forge a pact with and their powers show it. Especially the tentacles- there is a very heavy tentacle theme. They can create tentacles to attack their enemies and defend themselves and their comrades, they gain a swimming speed, the warlock can understand the speech of any creature while underwater and be understood by that creature, they have cold resistance, and they can teleport small groups of creatures up to a mile away from one water area to another.
(Player’s Handbook p.109) Warlocks bound to a fiend get some interesting abilities. They gain temporary hit points every time they reduce a hostile creature to 0 hit points, they can add 1d10 to an ability check or saving throw, they gain resistance to a damage type which they choose each morning, and they can send a creature which they hit in an attack tumbling through the lower planes for one turn.
(Tasha’s Cauldron of Everything p.73) Forming a pact with a noble genie seemed like a good idea to these warlocks. These warlocks can hide inside their version of a genie’s bottle along with a small group of friends, they do extra damage every time they hit with an attack, they can fly, they gain damage resistances, and they can ask their patrons for a 6th level or lower spell from any spell list once a day.
Great Old One
(Player’s Handbook p.109) Warlocks bound to a great old one can speak telepathically with creatures and the warlocks’ minds are shielded from being read. The warlock can force disadvantage on foes attacking them as a reaction, and if the strike misses then the next attack which the warlock makes on the foe is with advantage. These warlocks are resistant to psychic damage, and any psychic damage done to the warlock is also meted out to the creature which caused the damage. Finally, they can create thralls by touching incapacitated humanoids. Lots of mental options to be found with these Dungeons & Dragons 5E warlocks.
(Xanathar’s Guide to Everything p.55) Hexblade warlocks have made a pact with a being from the Shadowfell which provides magic to sentient weapons, hence the Hexblade name. These warlocks are proficient with medium armor, shields, and martial weapons. They do extra damage against enemies which they curse, they are much harder to hit by their cursed opponents, and they will heal a bit when their cursed opponent dies. These warlocks can also use CHA as their weapon stat when fighting with a weapon, and they can raise a person who they have killed as a specter which must then obey them.
(Van Richten’s Guide to Ravenloft p.30) Warlocks of the Undead have made a pact with a powerful undead, like a mummy or lich. These warlocks can take on some of the form of their patron, gaining them extra hit points, causing fear in those nearby, rendering them immune to fear themselves, and dealing extra necrotic damage in attacks. In addition, they don’t need to eat, drink, or breathe, can change attack damage types to necrotic damage, are resistant/immune to necrotic damage, when knocked to 0 hit points come back with 1 hit point while also exploding with necrotic damage which injures everyone nearby, and can send send their spirit from their body to get up to all sorts of mischief. Their disembodied spirit has a flying speed, resistance to bludgeoning, piercing, and slashing damage, and heals them when they do necrotic damage.
(Sword Coast Adventurer’s Guide p.139) Undying warlocks are bound to an immortal being. They learn the spare the dying cantrip, they have advantage on saving throws against disease, and they are difficult for undead to harm. These warlocks gain hit points when they succeed on a death saving throw or stabilise a creature with spare the dying. They can hold their breath indefinitely, they don’t require food, water, or sleep, they age at a much slower rate and are immune to magical ageing, and they can reattach severed body parts. Creepy, creepy party tricks.