Treasure Hunt – Use Mug when equipped and has node that gets Double Items – Beat Shinra at Sphere Break in the tournament and you win it while you’re playing the game
White Signet – Lets you use any learned White Magic abilities, nodes raise magic – Play the ladies’ dog during the Sphere Break tournament and win randomly during the game
Higher Power – Grid that allows you to Break HP/Damage Limits – Receive an Episode Complete for Clasko by finishing the mission in the Calm Lands dungeon
The End – Allows you to break HP and Damage Limits and spherechanging lets you use a special attack called finale – Really difficult, must oversoul every enemy possible in the game
Flash of Steel – Strength and Magic + 20, spherechanging also raises those stats – It’s one of the prizes for 200,000 credits from one of the Calm Lands companies, but you have to buy it before the two merge
Those are a few really good ones that you can get and don’t get automatically.
Shining Mirror – You only get this if you joined with New Yevon and then undertake a mission at the Youth League headquarters in Chapter 2. You can’t get it otherwise, unless you start New Game Plus.
Font of Power – You need to send out a high-level chocobo to the Mi’ihen Highroad and find the dungeon there. Then you have to beat the boss there in order to get it.
Oh, and here are a couple more good ones:
Megiddo – Lets you use Black Magic, nodes let you use Flare and Ultima – You need to jump down every one of the holes leading to the Farplane and make it to the end of the path on each one. Once you do that, your party automatically finds a treasure chest with it.
Supreme Light – Lets you use White Magic, nodes give you Auto-Life and Holy – Clear the Thunder Plains dungeon, I think
BTW, this isn’t all coming from me, just to say. I’m looking at GameFAQs and my official strategy guide.