Choco/MogShivaIfritRamuhTitanOdinKjataBahamutAlexanderNeo-BahamutLeviathanPhoenixHadesBahamut-ZEROTypoonKnights of the Round

Choco/Mog

Go to the Chocobo Farm and talk to the Chocobos inside the pen. They will do a dance and then give you the Choco/Mog summon.

Shiva

N/A (Priscilla gives it to you in Junon Harbor)

Ifrit

N/A (Jenova-BIRTH drops it after the fight in Junon)

Ramuh

YOU MUST GET IT AFTER THE FIGHT WITH DINE IN COREL PRISON, IN THE CHOCOBO JOCKEY LOUNGE. It's located in the corner, left and up of the sign that says Chocobo Racing.

Titan

In the destroyed Gongaga Reactor, after Scarlet and Tseng leave.

Odin

Unlock the safe in Shinra Mansion. After fighting Lost Number, you will get him. (If you need the code, check the "Secret Characters" section of my site.)

Leviathan

After defeating Godo in the Pagoda at Wutai, you'll receive it.

Bahamut

N/A (after defeating the Red Dragon in the Cetra Shine/Temple of the Ancients)

Kjata

In the 2nd section of the Sleeping Forest, you'll see a red materia dropping out of the trees, then going back into them. Catch it to receive Kjata.

Alexander

This one is hard. Walk around in the Great Glacier until you find water that has a lot of steam coming out of it. Touch the water. From there, walk straight up to the area where the wind blows and it looks like you are on the world map. Place markers with Circle, and walk straight until you see a cave. DO NOT ENTER IT. Turn right, and walk straight until you are back into Great Glacier. When you reach the area with 2 exits and 1 entrance into a cave, walk into the cave. Talk to the woman, defeat her, and you will get Alexander.

Neo-Bahamut

On your first visit to the Crater, in the first section of it, you should see a red materia near the bottom of your screen. Pick it up, and you now have Neo-Bahamut.

Phoenix

On your last visit to Fort Condor, after the battle, go out to where the giant condor was. Look around until you find the red materia. You can do this during or after the final Fort Condor battle.

Hades

After gaining control of the sub, head directly west of the Underwater Reactor. You will see a crashed gray airplane. Enter it. Go straight, past the treasure chest. If you haven't had your final battle with the Turks, you will have to fight Reno and Rude in the hallway. Walk through the next doorway. You will see tons of items. Walk down the stairs and you will see a red materia by the helicopter. Grab it, and you will have Hades. WARNING: SAVE BEFORE LEAVING! EMERALD WEAPON MAY BE RIGHT OUTSIDE THE DOOR! He WILL kill you!!!

Bahamut-ZERO
When you return to Cosmo Canyon and Bugenhagen shows you the model of the planets, look at the blue Huge Materia and you will receive Bahamut-ZERO.

Typoon

In the Ancient Forest, get to Area 3 and follow the limbs all the way up and to the right. you will see it there.

Knights of the Round

Now, THIS is the best summon in the game. You MUST have a gold chocobo to get it. In the North-Eastern part of the world map, you will see some islands. Go to them. Then, ride your Gold Chocobo North-North-East and you will see an uncharted island. Ride your chocobo into it, hop off, and go into the cave. You will see a red materia. Grab it. You now have the BEST attack in the game. So, you want to know what it does? Well, 13 knights attack 1 or all opponents with about 7000-9999 damage for EACH knight. Plus, the effect is cumulative, AND the attack is focused, causing it to do the same amount of damage to all enemies or just one. For example: you are fighting 5 headbombers. KOTR deals 9,999 damage THIRTEEN times to all enemies. Example 2: you are fighting Safer-Sephiroth. KOTR deals 7000-9999 damage THIRTEEN times on him. So, KOTR deals between 91,000 and 129,987. (excluding enemies with barrier on them.) Pretty awesome, huh? Heheh.