If you wish to see a dead person again, you must seek a Reaper. These psychopomps may be found in ancient necropolises, or temporarily at sites of many deaths. In exchange for capturing ghosts that evaded their grasp the first time, they will present you with a dead person for a visit. You can touch the dead soul, speak to them, but they owe you nothing beyond what you can offer a dead man.
If you need a huge sum of cash as fast as possible, you must seek a Dragon. They are always found at the top of mountains or far, far away. Dragons may offer loans to those who can offer the right collateral, but there is no guarantee you can pay them back. If you fail to make back your payments even once, the dragon will destroy everything you hold dear.
If you want to regain lost youth, you must seek a Fairy Queen. They like to collect the years of mortals, freely given from endless summer dances or enchanted slumbers. You must never take anything they say as truth; you may ask for a few years left to live and they may give you the last years of a crippled beggar. Stealing the years yourself is more sure, but then you are stealing from the Fae, and they will never stop hunting you once they know your theft.
If you wish to go back and fix your mistakes, you must seek a Weaver. These huge black spiders are old as time, and can weave the strands of fate which tie you to your choices. They can make new weaves, or break old ones, but never give anything for free- there is nothing you can offer them that they could not already acquire from a sudden turn of fortune. It is unknown how many times a Weaver has worked its craft, because each time history is rewritten and the old past is forgotten.
If you wish to fly to a land you could never reach, you must seek a Pegasus. These are proud horses, magic, and holy. They are almost impossible to catch, and impossible to tame. If you can jump on ones back and guide it, it can take you anywhere you could possibly want to go. The moment you step off, it will abandon you, and you will need to find your own way home.
If you want a truly fearsome weapon or piece of armor made for you, you must seek a Cyclops. They are the greatest craftsmen in the world, but are monsterous and man-eating creatures. You must put the idea in its head to craft the object and supply the materials without it laying eyes on your once. Each Cyclops is incredibly jealous and possessive; you will not be getting the item back without silent feet or great force of arms.
If you want to remember something you forgot, or find something you lost, you must seek out a Sniffer. Smell is the strongest scent tied to memory, and they will make you remember. They can only be found in the darkest place in the Earth, and their appearance and habits are enough to drive away almost all seekers. They can help you remember things you never thought before; like what you thought before you were born.
If you want somebody dead, then you must seek the Hangman. These beings exist in every great hall of a lord, or within every prison, hidden away and out of sight. You must make your case for the person's death, as well as the time and method that it is feasible. They will only target the guilty however, and if your sins out weight the accused, the hangman's noose will slip around your neck instead.
If you wish to know the great old truths, you must seek a great old Sphinx. They are not common to give up the truth, and not all Sphinxes know it. You must outwit them, upon a killing blow the Sphinx will die with all secrets on its smiling lips. Those who seek the meaning of life, or the truth of their birth, are to be wary. Not all knowledge brings joy.
If you wish to elevate your blood from the common stock to the noble, you must seek the Lady in the Lake. She will only show herself to those who will right the wrongs in her land. To some, this means that only the noble-blooded by birth will find her in the first place. To others, this means there is really no difference between the noble and the common at all.
If you wish to learn the most powerful of the hidden blade arts, you must seek an Ascetic. They can be found anywhere there are the poor and wise. They reject all material things and sensual pleasure, and as such will not exchange their knowledge for what you value. They can smell ambition like a dog smells blood, and will not teach to one who is not willing to learn the true lesson they preach.
If you wish to change the world in some other way, then you just need to seek a Genie. They won't cost you anything, but are harder to find then all of the ones above. Everything within their power is yours, but you must follow their rules. Just be careful what you wish for.