To read the cheats, right click on this page and choose Select All(don't click again or else you'll have to do this Select All stuff again). Be aware that not only does this contain cheats, it also contains spoilers.
Lots of EXP: Go to the Chocobo Stables, and walk around on the Chocobo Tracks. You won't encounter no chocobo, but you may occasionly encounter an enemy called EXP Holder. He gives you lots of EXP, but the chances of encountering him are around 1 in 30. You can also encounter them in the cave near Mideel(you used to get Quadra Magic there). You can also encounter Pig Bombs in the cave, but beware that you encounter enemies almost every step in there.
Protection Ring: In the Temple Of The Ancients, at the second save point, go left then down. Press enter at a place where you can't go down any further, even though you should be able to. You'll get a Protection Ring.
Easily Defeat Stephen: Well, maybe not Easily, but Easier. You're allowed to lose to him once without getting game over, but you get game over the second time. However, the second time he'll only have 900 HP, where he has 1100 HP the first time.
Pearl Weapon's Weaknesses: Do you keep dying to his Pearl Blast attack? Well, if you use Magic Shatter on him(fight Kill Devil to get it), he can't use any attacks except Kill and a regular attack for the rest of the battle(he may try to recover MP, though it's unlikely - and plus, it would take three ethers to be using pearl blast again anyway, because pearl blast takes 214 MP). Also, if one character has no non-elemental magic, and their attack isn't good enough, Pearl is weak to Lightning and is effected by(but not weak to) Ice and Earth.
Get Beta without fighting Midgar Zolom: You can also learn it from Kill Devil, Crystal Weapon and Stephen. Oh, and from Fire Box. And if it being available from Midgar Zolom didn't give it away, you can get it from Cosmo Zolom.
Pig Bomb Warning: If you play multiple times, the password is random out of EAT A ROCK, SMELL MY FOOT, GET LOST COWARD and TEMPLE OF ANCIENTS. So don't try reusing the same one. Also, random guessing works if you want - nothing happens if you fail. The password, btw, is found between the two rocks near the switch to open the door. Stand there and press enter. You need to read it 16 times if you haven't found Pig Bomb yet, so it's easier to find Pig Bomb, then go back, so you only need to read it once. Also, keep reading it to get a Phoenix Up. Keep reading it more to be able to check what it is once again.
Ancient Water Effects: The effect depends on what you do. If you touch it, your HP, MP, Magic and Speed go up while your Attack and Defense go down. If you drink it, your stats go up and your HP and MP go down. If you look at it, you get a full recovery.
Annoy Bug Notice: When you have to fight them in Temple of the Ancients, you can run from them, but if you run they'll still be there. Also, you may notice that you can't get rid of the ones on the far left, thus making you unable to get to Kill Devil(and the door, later in the game). Well, the way to get rid of them is to get rid of all the other three. Also, if you encounter them in groups of two, just kill one, and only kill the other after it uses Inflictor - because Inflictor is an enemy skill, and a very good one too. It helps you A LOT when fighting Kill Devil - even though it isn't anywhere near full power, it's powerful enough. Note that there was a bug with Inflictor in the first version but it's fixed in the second version(it was that sometimes you get game over after either you or the enemies use inflictor).
Kill Devil's Magic Invincibility: You may have noticed how Kill Devil is immune to elemental weapons and all magic/enemy skills. Well, there's exceptions. The first is Inflictor, as mentioned in the previous cheat. The next is Drain. Also, he isn't immune to MP Dust. He wouldn't be immune to Magic Shatter, except you can't get it without beating him anyway. He can also be effected by Ancient Flash. But that's the lot. By the way, he's immune to most status effects, but you can still hit him with Mini, Slow, Darkness and Poison(not poison elemental magic though).
What to do after Temple of the Ancients: When you're done there, return to the Chocobo Stable. Talk to Choco Billy, then head to Fort Condor. Talk to the guy who you talked to when fighting Crystal Weapon, then finally return to Choco Billy. Then head for Temple of the Ancients again. You should be able to work out the rest.
Junon: There's nothing worth doing here - especially after defeating Pearl Weapon. But before defeating Pearl Weapon, there's an Inn and a Materia Shop. Also, the Weapon shop will be selling the best armour in the game, but it costs 500000 gil. If you miss it, you can buy it later. You can get into Midgar after Junon is destroyed - go to one of the smashed signs and press enter. Now you can get into Midgar, but you can't go into the city.
How to exit Temple of the Ancients(first time): On your way out, search the first treasure chest again(the one you got the Phoenix Up and Megalixir in). You'll recieve a Phoenix Megalixir(the only one of it in the game). Now, if you go up to the next floor, a new pole will be there. Climb up it to leave.
If that isn't enough, click here for a walkthrough.