Oh, I forgot!!
There are 2 things we didn't do! Vancian Magic, and Energy Pool magic (where casting a spell takes energy from a pool).
Here they are, with options being mostly interchangeable:
VANCIAN: Characters can prepare spells up to 5 times their rating in a given art. Preparing a spell takes as long as a ceremonial casting.
Option: Trading Arts: you can convert slots from other arts on a 1-to-1 basis. That is, you can use a rating of 10 in aquam to prepare 10 levels of Terram spells, not 50.
Option: Long Prep Times: preparing a spell takes as long as a ritual casting
Option: Dying Magic: Preparing a spell requires the expenditure of vis: 1 pawn per 10 levels. Double the cost of rituals
ENERGY POOL: You've got a pool of energy points equal equal to twice your total rating in arts. To cast a spell, spend energy equal to its level.
Option: Fire for Fire: You have separate pools for each art, following the rules for Vancian Magic, above.
Option: Building inner magic: Add 5 times your Warping (or Corruption! ^^) score to your Energy Pool. You can also use this as "free slots" for vancian magic, above
Option: No Free Lunch: Spells are cast with Pen 0. If you want more penetration, you must spend 1 energy for 5 pen, up to your Penetration total
Option: Places of Power: An aura contributes energy points equal to its bonus to spellcasting.
Option: Dead Magic: If the aura gives a malus to spellcasting, you must spend as many energy points.
Option: Items of Power: An enchanted item can store energy points. Use ReVi to build a spell container. Each EP takes 5 levels. Recharge may vary: 1pawn per 2 EPs, sunrise, season, year... You may want to tie this to an aura, like Aura bonus per day
Option: Divine Magic: Energy Points must come from a god or spirit, who spends might. An interesting option is to make these come from the familiar only, making one a requisite for spellcasting
To regenerate your energy pool, you may spend 1 fatigue (gives 5 points of energy) or rest an entire night.
As a matter of taste, I like the No free Lunch option (One thing I'd love to see in a magic system is 2 pathways: raw force or skill, with some ways to trade one for the other. Arts mostly embody both, which, IMO, is a loss), Places of Power, and Items of Power.