I'm working on a new spell point system, which seems pretty smooth so far...
Each spell is worth a number of points equal to its level, and a character, cleric or magic-user, may select spells that equal his total spell points.
For instance, a 3rd level magic-user is able to cast two 1st level spells and one 2nd level spell. His total spell points equals four [(2x1)+(1x2)=4]. So instead of memorizing two 1st and one 2nd level spells, he may memorize four 1st level spells. He may not, however, memorize two 2nd level spells. As he progresses in experience, this principal stays the same, being able to memorize more lower level spells than is normally permitting, but not higher level spells.
So, for a second example, Bushka the 8th level magic-user can normally memorize the following:
1st Level: 3
2nd Level: 3
3rd Level: 2
4th Level: 2
However, under this system, Bushka has a total of 23 spell points. He may not use them for more than two 4th level or 3rd level spells, but may memorize more than three 2nd or 1st level spells, if he wishes.
Now that I'm writing this out, it doesn't sound so simple! I'm going to have to test this a bit in real play and see how it pans out. Off to the gaming table!