How many alternative magic rules do you know? The more you know, the more ideas you can compare, which means contemplating rule changes, which aren't proposed here.
For starters, look at these books: Monte Cook's Arcana Unearthed, Unearthed Arcana, Expanded Psionics Handbook and Elements of Magic: Revised (PDF only) change the assumptions more or less. Arcana Unearthed has three layers of spell in every spell level - simple, complex and signature. If you know a layer of spell level, you know every spell of it - like a cleric. But you select every day a certain amount of spells of them, which you want to be
able to cast for that day. Then you can cast the chosen spells like a sorcerer.
Unearthed Arcana has a spell point system, which are like power points. You choose your spells (I don't have UA, so I don't know details) and cast them spontanously. You have to spent extra points on a spell to raise the caster level, so even a 10th level wizard tosses 5d6 fireballs, even he doesn't want to spent more or want to save spell points for another fireball.
XPH is the second most flexible system of all - UA being last. It allows to augment powers, like UA, but has more options for every power than merely a raising of the damage. But the king is EoMR - it is two or three steps more flexible than XPH. It uses magic points and spell lists - the latter can be combined to define spells, which can be spontaneously cast. I believe, that EoMR qualifies as the best basis for a skill magic system of all systems, I know of. Maybe in the successor of EoMR, Lyceian Arcana, a skill based system is included, but I'm not sure about that. For more infos about EoMR look here:
http://www.enworld.org/reviews/index.php?sub=yes&where=currentprod&which=EoMRE