That is one of the things I liked about Monte' Cook's magic system in Arcana Unearthed. Each spell, besides spell level, is set up in three broad catagories. Simple, Complex, and Exotic. Simple spells tend to be not as powerful as Complex or Exotics, and exotics tend to be fairly powerful for their level and require a feat to learn to cast them (like Exotic Weapon feats). With in each spell you have the base power, which you cast at the spell level. Diminished power, allowing you to caste the spell at one level less, taking a lower level slot, or at heighten power which takes up a higher level slot.
Also you have so many slots per day but you don't memerize spells. You have a separate number of prepared spells per day, but you can use up all your slots on one prepared spell.
It is a fairly nice system.