I like Vancian magic, but I have thought about different systems. I've especially thought about changing the way divine magic works and the best way to implement psionics and chi powers.
One thing I have considered is introducing ritual magic, like in 4th Edition. This magic may be completely separate and incompatible from Vancian-type magic, or a different expression of that kind, or a seperate discipline that is nonetheless used alongside Vancian magic.
In a similar spirit to my splitting of the fighter class I am considering using not one, but multiple magic-user classes. There would be an illusionist class, also having skill in charm and compulsion-type spells and a necromancer class, but also perhaps having a "white mage"-like variant that heals and reinforces his allies. I very much like the summoner class that Paizo recently developed for Pathfinder. I also have other ideas, like a warmage (evocation specialist, but also like a fighter/mage), a shapechanger and a savant (divination, primarily). That's also only getting into the wizard-like classes, I also want new theurge/priestly classes, probably along the lines of specialty priests. But I have a sort of problem. If there's all these specialized classes what class is Mordenkainen and Bigby? The obvious answer is of course "wizard", but what is a wizard? I don't want to have a generalist class, but what else are archetypal wizards? With the fighter I had the same problem, except using Yrag and Robilar as my examples. I came up with a solution in that case but I'm not sure what to do with the wizard.