I hinted in the post on Vancian magic vs. spell-point magic that there are other possibilities for magic systems. Three possiblities, from what I can see. I'm going to be silly and call them Failure, Fatigue, and Fetishes.
"Failure" means, essentially a roll to cast spell system. There is no spell memorization or spell point cost. You can cast a spell as many times as you wish, but you have to roll for each time you cast the spell. There may also be an extremely undesirable fumble result. This may be a skill system, with one skill per spell, or it may be a unified roll, such as the Clerics Without Spells approach.
By "Fatigue", I don't mean a spell point system that labels spell points "fatigue", as in TFT/GURPS. I mean that you have a simple two or three-level system of physical conditions, like "normal", "tired", and "exhausted". Possibly, there's a "Failure"-like roll to see if a caster drops to a lower energy state. Spell casting becomes diminished or impossible at some energy levels.
"Fetish" is just my cute way of referring to a spell component system. Instead of spending abstract spell points, casters "spend" physical resources. Basically, it's a spell-point system where the spell point pool is your money, The simplest way to do this in D&D is to adopt the Holmes rule about magic scrolls and forget about spell memorization: spell casters cast spells by reading scrolls, and you can cast as many spells as you can carry or afford. Other options would be to use potions (which, I've heard, is how Arneson did it originally) or inherently magical materials. I based the alchemist/witch around this idea, and mixed it with X Without Spells for the necromancer.
As I said before, I find it odd that, even though each of these systems has been suggested in one way or another, anytime someone posts a vehement diatribe about Vancian magic, they always suggest spell points as the only viable option.