Well spellcasting is based on setting. There are a few examples for the urban arcana setting: The mage and the Acolyte.. basically modern, depowered Wizard/Sorc and Cleric.
Spells per level are lower, but that has more to do with the fact they are advanced classes. None of the d20 classes go higher than 10 levels at this point.
Something I didn;t think I'd like, but after reading more of the book I think is a great idea to approach a more 'classless' d20.
Strange that the fix for classless d20 would be to add more classes isn;t it? But I think it works.