I have always wanted to like a spell point system, but I don't. I think it bothered me because I just wanted to fire and forget. Tracking slots is so ingrained in my head, doing something different can be hard. Having said that, I think I found a system that just works for me.
I posted some of this as a comment on G+ already, but I expanded it here to be able to explain a few things more clearly. As always, the first option does not make use of my Emphases System. It is so similar to a comment that +Joey Mullins said here, that I am linking to him and the post that holds his comment.
I call magic-users on a spell point system sorcerers. I list them as a separate class with separate advancement tables. In my mind, it prevents me from confusing which character is using Vancian magic and which one is adding up points.
Spells have a point cost equal to the spell's level. The amount of spell points a sorcerer can have is located on the advancement table. As spells are cast, the player totals the amount of spell points or mana used. If that total is equal to the number listed on the advancement table, it will take 8 full hours of rest to be able to cast spells again.
The difficulty to cast a spell is 11+spell level. The sorcerer gets a bonus from INT and his or her level to a 1d20 roll. This means that if you have Roy, a 1st level sorcerer with an INT 15 attempting to cast Magic Missile, he must meet or exceed 12 on his roll. He gets a +1 bonus due to his high intelligence and also gets to add his character level, another +1. Roy rolls 1d20+2 greater than or equal to 12. For those that care, he has a 55% chance of success.
I have an more involved version that uses +Peter Fitzpatrick 's idea of having 20 levels of spells instead of 9. All the standard S&W spells are given new levels (i.e. Wish is a 20th level spell, Fireball a 5th level spell) The difficulty to cast a spell is saving throw + spell level. The sorcerer gets a bonuses from INT, his or her level, and specializations to a 2d12 roll.
Let's take Bob, a 1st level sorcerer with INT 15 that specializes in Detection spells. Since he is 1st level, he gets a +1 to roll. With an INT 15, he gets another +1 to the roll to cast any of the canonical spells in S&W. He also has a specialty in Detection that grants a +2 to the roll for detection spells. So when Bob attempts to cast Detect Magic, a 1st level spell, he rolls 2d12 + 4 to beat or exceed 16. However, if he attempts to cast Magic Missile, also a 1st level spell, he has to roll 2d12+2 to beat or exceed 16 because Magic Missile is not a Detection spell.
At every level, Bob can increase an existing specialty by 1 or gain a new one at +2. So if he reaches 2nd level, he can increase Detection to a +3 bonus, or grab a new specialty at +2. These specialties also come into play for spell research, so it makes for some really interesting spells.
Regardless of which variation you use, here is the Progression Table of the Sorcerer. All other rules for the magic-user apply. The GM may choose to say that Sorcerers do not use spell books and that 8 hours of sleep refreshes the ability of the sorcerer to cast spells.
Standard Sorcerer Table
Next time, I hope to do more with creating magic systems. Game Knight Reviews mentioned this project on G+. Like I said there, I hope to provide examples of building magic systems soon. The next post, however, should be an alchemist.