This is to help you receive every Aeon in Final Fantasy X. It is recommended that you do the sections in order as that is the order they will need to be done in. If you have already achieved any certain Aeon, please overlook that section.
Yojimbo is the first secret aeon you can get and the only one who doesn't require the airship. First, go to the gorge in the Calm Lands and enter the Chamber of the Stolen Fayth. Note: Beware of some of the fiends in here if this is your first visit. Fiends too avoid include: Magic Urn, Dark Element & Ghost. Proceed to the far end of the cavern until you see a warp pad. Step on it and warp to the Chamber of the Fayth. Inside you will meet Yojimbo. Yoou will have to pay him for his services, not to mention every time you use him in combat. To receive his lowest initial price, answer him, "To defeat the most powerful of enemies". Now every time he asks a price, bid half of his initial price, plus one. Next time, add one more Gil to your offer. By the time he proposes 200,000 Gil, he will generaly accept prices below that, though not by much. If at any time you bid at leats triple his initial price, he will give you two Teleport Spheres in addition to his services.
Anima is probably the most difficult Aeon to unlock, but well worth it. First, you will need the airship. Enter the hidden coordinates, X: 11-16, Y: 57-63 to unlock Baaj Temple on the airship. Head on over to Baaj and you will encounter an old foe.
Geosgaeno will attack with Stone Punch and KO Punch, two very devistating abilities, so equip Rikku, Tidus and Wakka with armor bearing protection against Petrification and Death before entering Baaj Temple. Cast Hastega and Protect on the entrie part and make sure you use everyone's Overdrives whenever you can. Geosgaeno is weak against every element so use alll of your Fire Gems, Ice Gems, etc. on him.
Baaj has gotten smaller since your last visit. Proceed to the back room and touch each oof the statues. If you did not receive every item from every temple, return to Bevelle to witness the events pre-end of game time. YOu should now be allowed back in the temples so return to any temple whose glyph did not appear and receive all the items within. Return to Baaj and touch each of the glyphs once more. You will proceed to the Chamber of the Fayth where you will meet Anima's true face, Seymour's mother.
The Magus Sisters
In order to unlock the most powerful Aeons in the game, you will need two items, the Flower Sceptor and the Blossom Crown. First, go to the Calm Lands and find the man on the Chocobo. Ask to ride a Chocobo and ride to Remiem Temple. Defeat all of Belgemine's Aeons up to Bahamut to receive the Flower Sceptor. Now go to the monster arena and buy weapons with the Capture ability (I recommend adding the Sensor ability to all of them). Go to Mt. Gagazet and capture every type of fiend there, including the ones in the cave. Return to the monster arena and the man should produce the Blossom Crown. Make sure you have every other Aeon. Return to Remiem Temple and touch the glyph on the back wall to receive the Aeons. Now all you have to do to receive another great item is defeat the rest of Belgemine's Aeons.