The following hexes are adapted from the seven voyages of Sinbad the Sailor. In some cases I have done minor adaptations to make it more D&D-like. When hexes are on the same island I will not so with a parentheses next to the XXXX entry.
XXXX What appears to be an island is actually a fish of enormous size that has slept for many years. Sand has accumulated upon it and shallow rooted jungle trees have even taken root. Should any fire be set on the fish, or perhaps an anchor stuck into its side, it will awaken and return to the bottom of the sea. Anyone on the island when this occurs must make a Saving Throw or be swallowed up by the sea, starting the next round 100' or more below the depths. Those that succeed tread water on the surface. Heavy metal armor will cause an automatic failure. Should the creature be attacked, it has 36 HD. It is easy to strike, but only weapons with a +2 or higher bonus or that are meant for sieges (such as a cannon or ship's ballista) will damage it.
XXXX This heavily wooded island has a wide shore. A beautiful black mare has been tied to a stake in the surf. Anyone approaching the mare will be beckoned by a man who waits unseen at the shore. He well ask the characters to wait with him in a underground chamber. He is a groom of the king of the city in hex XXXX. He is awaiting a hippocampus to come and mate with the mare. Any foal born of such a union will be able to gallop tirelessly, having double movement speed in overland travel. If the characters refuse to wait with him, he will bang his shield and summon his 6 fellow grooms (HD 1+1, AC 15, armed with spears and daggers) to attack.
XXXX This island is the home to a mated pair of rocs. They spend the daylight hours hunting the giant snakes that live on the island in hex XXXX (see below). The island has three eggs buried partway in the sand and those not expecting such eggs my believe they are domed buildings without obvious entrances. Should the egg or hatchling of the rocs be taken to a noble or king rich enough to afford it, each of the three will fetch 3000gp, though woe be unto the noble who buys them. Should the eggs be struck or stolen, the rocs will attempt to sink any boat belonging to men associated with the act. A negative initial reaction roll will mean that the rocs think that a ship could serve as a meal. Unless their children are disturbed, the rocs are unlikely to pay attention to individual humans.
XXXX (Isle of Gems) This hex is full of a sandy desert infested with giant, venmous serpents (HD 4+2, AC 14). The snakes rarely emerge during the daytime due to fear of the rocs in hex XXXX (see above). Anyone wandering through the desert at night will encounter a snake for every 5 minutes of travel.
XXXX (Isle of Gems) The mountains in this hex are jagged and difficult to climb, but their heights are covered with gemstones (tigers eye if you're feeling cheeky). A group of merchants who know the secret way up the mountain through the skinned corpses of sheep down the mountain to collect the gems. Anyone who does so, or finds a sheep thrown by another person, will get 250gp in gemstones.
XXXX (Isle of the Apes) The shore of this island is home to 300 ape-men (HD 1+1, AC 14, Claw 1d6 or weapon) who can climb with such alacrity that they can easily get onto a ship even from the swirling ocean. They will cut the sails and ropes of any boat as well as carrying away any goods or treasure aboard. They will ignore anyone who does not attack, but if one is struck all the apes will move to attack the assailant if possible. They lair in a subterranean village, where they hide from the giant (see below), and have collected 1000gp in spices and other goods. No one is certain what they do with it, even seemingly the ape-men.
XXXX (Isle of the Apes) A large "abandoned" manor serves as the home for an adolescent giant and his mother (as Hill Giant and Stone Giant). The mother is rarely seen unless the adolescent is injured. The adolescent scours the island looking for people to eat. He will select the heaviest member of any party to take home and roast on a spit. He will only attempt to seize his potential meal and if attacked by others or injured will run to his mother. There is furniture in the manor worth 2500gp, and a +1 set of greek armor (as plate).
XXXX (Isle of the Cannibals) This small city of c. 1,500 is inhabited solely by cannibals and the Type IV Demon that serves as their king. The king usually operates under an illusion to make him appear as a mortal, but the scent of death is always present about him. Anyone who eats food prepared by the cannibals or presented by the king must make a poison Saving Throw or lose all sense and wish to do nothing more than eat. The first meal of each day prompts a new saving through, but with a penalty equal to all previous meals consumed. Eventually those stricken begin to resemble cattle and eat grain out in the fields, watched by cannibals. These victims are eventually slaughtered, their blood and organs fed to the demon and their flesh devoured by the cannibals.
XXXX (Isle of the Cannibals) This city, also of around 1,500 inhabitants, is much more innocuous than the city of the cannibals; however, it has a macabre tradition. Whenever a man or woman dies, they are lowered into the catacombs beneath the city along with their possessions and their living spouse. Some of the spouses have tried to form gangs in the underworld, killing newcomers for the little food and water they are given. An entrance to these catacombs exists on a cliffside facing the sea and is unknown to the inhabitants of the city.
XXXX This island seems like a lovely paradise - temperate but warm weather, sweet flowing streams, plentiful fish and fruit. Its sole inhabitant is the Old Man of the Sea (HD 4, AC 10, 1d6 damage with both fists, immunity to nonmagic weapons). He will ask to be helped up onto the back of anyone unfortunate enough to meat him, so that he might cross a stream he sits in front of. Once on the victim's back he will refuse to remove himself, forcing the character to move as though encumbered and in heavy armor, and will constantly gode and strike the victim into doing his bidding. It is impossible to remove him unless he sleeps, which he only does if he drinks alcohol. He has never actually seen alcohol before so does not know of this effect. This slumber also removes his immunity to magic weapons.
XXXX The area around this island is a set of doldrums which will permanently entrap any boat with sailors not adept enough to avoid it entirely. Once trapped the only option, baring magic or player ingenuity of course, is to set down on the nearby island. It is rich in natural resources, gems, gold, silver, and ambergris which flows out of a geyser for some reason. However, the island lacks any forms of food. A stream on the island leads into a dark cave that, if traveled long enough, leads through the earth and into hex XXXX, but it becomes so narrow that anyone attempting to make it through with treasure will at best only be able to come away with 1000gp in goods, and that is if they can think of a way to avoid bringing food on the journey.
XXXX This city of 666 buildings is actually home to 666 vrocks masquerading as humans. They will do little to reveal their nature, but will also refuse to allow any to leave the island. A family of humans dwells hear in fear of the vrocks, but they know a secret that can destroy them: causing the vrocks to fly into the sky will make the gods of good and light aware of their presence and bring down a cleansing fire.