My current ideas on spellcasting mechanics.

For some fun I have been writing up a document with a bunch of my ideas for DnD next. I had started about the time the first playtest packet came out. I've been updating it ever since. Most of it pertains to the class and spellcasting system. I just submitted it to my blog, I had to split them up into 3 pieces for them to be submitted properly.

My blog entries are right here. I am still trying to format them to look better.
community.wizards.com/cerius/blog/?pref_...

I have a non vancian mechanic for the sorcerer, warlock, bard, and druid. The cleric has the 'access all divine spells, cast spontaneously by using a slot of level n or higher' mechanic. The paladin and monk are pretty traditional.

You don't need to have too many slots to keep track of in the case of the wizard. Spell slots become at will at higher levels. Clerics don't have their power getting out of hand by phasing out lower level slots, this isn't much of an issue given that they can use higher level slots to cast spells, and they tend to get similar but more powerful versions of the same spells anyway at higher character leve.

What I like the most are my warlock and bard spellcasting systems.
The warlock knows a small set of spells in addition to the powers they get. They can attempt to cast these spells with no need of exhausting slots or spell points, however they must make a die roll (perhaps at advantage or disadvantage) to see how well it's cast and what downsides they may get. In a sense the warlocks are 'hacking' into the traditional forms of spellcasting, but it's dangerous.

Bards 'charge up' chains per round, which they can then end to cast a known spell of level equal to the length of the chain. Only a certain number of chains until a long rest are allowed however.

The druid is a hybrid encounter/daily spell point system, and is still a work in progress.

The spellcasting mechanics for some of these classes can be placed on some of the other ones. Perhaps you want the preparation of spells mechanic of the wizard and the casting mechanic of the warlock, it should work but is probably overpowered.