Materia and Magicite
Since I'm at work, I'm gonna use the forums to post my chicken scratchings regarding Materia and Magicite.
With Materia, I plan on having a few different categories or types:
One type of Materia will allow you to learn spells. I think I'm going to make this Materia varying shades of red.
These spells can be cast either through MP or through prepared or memorized spells per day. This allows all characters to cast spells, while still making primary spellcasting classes the powerhouses of magic. These learned spells will require xp expenditure to learn, and unless the character prepares them as Divine spells (or casts them as an Oracle with MP), these spells will be cast as Arcane spells and subject to arcane spell failure, as per normal.
One type of Materia will allow you to manifest minor special abilites, ranging from emulated feats to spell-like abilities to more power powers. I think I'm going to make this Materia varying shades of blue.
Some of these abilities won't require any expenditure on the part of the character to activate; in essence, these could either be always on or usable only a certain amount of time each day. Other of these Materia would require MP expenditure, or even AP expenditure. This allows most characters the ability to use these powers, while still making some classes able to potentially benefit more from them than others.
One type of Materia will allow you to modify the properties of your items. I think there'll be three types of this type of Materia, and each type will have a different color range.
One type will be a clear color, ranging from perfectly transparent to a very cloudy white/grey color. These Materia can be used in creation of items, permanently modifying the properties of the item. These Materia would likely be the cheapest, as they can't be reused. They would grant various abilities, but would most would mimic standard D&D magical '+1' (or better) bonuses.
One type would be a greenish color. These Materia can be used in Materia 'slots' on items, namely weapons and armor. These Materia alter basic properties of the item, such as making the weapon deal fire damage as well as slashing, or making an armor's AR apply to cold damage as well as normal damage. These Materia will carry a fairly large price-point, due to their ability to be used over and over again, with varying effects.
One type will be any variety of color, making it difficult to determine exactly what any given Materia does. This type of Materia can be 'attached' to a piece of equipment, such as weapon or armor, but does not require a 'slot' to function. These Materia would be some of the most expensive, because there's not much limit to how many can be attached to any one item. Their abilities could range from the most basic magical '+1' bonus, to additional dice of damage, to changing the item's properties entirely.
Magicite will work a lot like the blue Materia; it'll grant you abilities whenever you use it. However, Magicite is far more powerful, and works more like a 'template' that is applied to whenever your character uses it. Materia requires AP to use, and lasts for a certain number of rounds. Magicite will range greatly in color, and it's unknown if there's any correlation between the color and the properties the Magicite grants.
A whole esper soul would function similar to D&D artifacts and range in size greatly depending on the power of the esper it belonged to. Possible uses for a whole esper sould would be to summon the esper itself for a certain period of time to unleashing large amounts of its power in the form of spells, or even transforming the user into the esper, granting it new life.
I'll follow with some example pieces of Materia, because work is just that slow today.

Materia and Magicite
All gil values for Materia are approximate; Materia is rarely sold, and if it is, it often goes for much more than 'reasonable' price.
Spell Materia (Red):
Spell Materia contains a single spell in each shard. To learn the spell costs 100xp * spell level^2 as well as 1 day of study per spell level (a 0th level spell costs 50xp and a day of study). Spell Materia's shade is dependant on the spell level of the spell it contains.
Dull red, 0th or 1st; Pale red, 2nd or 3rd; Dark red, 4th or 5th; Pure red, 6th or 7th; Bright red, 8th or 9th.
Cost: 22,500gil (0th); 45,000gil (1st); 110,000gil (2nd); 195,000gil (3rd); 300,000gil (4th); 425,000gil (5th); 570,000gil (6th); 735,000gil (7th); 920,000gil (8th); 1,125,000gil (9th).
Poison Materia (Green): Socketable
Poison Materia has two different effects; one when socketed in a weapon, the other when socketed in armor. When socketed in a weapon, the materia applies a dangerous poison whenever the weapon deals wound damage. When socketed in armor, the materia grants a certain level of protection against poison. Its effects vary depending on the color of the materia.
Dull green, +1d6 initial and secondary wound damage (Fortitude DC 13) or poison resistance 2; Pale green, +2d6 inital and secondary wound damage (Fortitude DC 15) or poison resistance 5; Dark green, +3d6 initial and secondary wound damage (Fortitude DC 17) or poison resistance 10; Pure green, 3d6 initial and secondary Con damage (Fortitude DC 19) or poison resistance 15; Bright green, 4d6 initial Con damage and death secondary (Fortitude DC 21) or poison immunity.
Cost: 345,000gil (dull), 1,200,000gil (pale); 2,700,000gil (dark); 4,800,000gil (pure); 7,500,000gil (bright).
"You see now they're thinking about banning toy guns... And they're going to keep the fuckin' real ones!"
Repeating this will totally get you laid.
Materia and Magicite
this totally rocks. with the explanations you've given here, i am more interested than ever before in playing. awesome dude.
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