I've been quietly watching this thread, but no one really seems to be articulating two salient points, especially in light of Patryn's concern that the wizard should be able to cast an essentially infinite number of spells each day.
1. D&D, from its inception, was based upon military wargames. Just like in a real war, your PC goes into the fight not with the resources he wants, but with the resources he has. More importantly, wars are just as much about managing your logistics as it is about killing the enemy. Don't have any more Fireballs memorized? Use something else or get out of the way of the fighter. Don't have *any* spells memorized? *Stay* out of the way of the fighter. The fighter is down to 10 hp? Retreat. The fighter drops? Run!
2. Just because the fighter can attack every round or the rogue can attempt to hide in shadows every round doesn't mean that the wizard or cleric should be able to cast spells every round of every combat. What does the wizard do that no one else does? He handles all of those utility tasks *outside* of combat - identifying magic items and crafting new ones. The cleric? He can turn undead without casting a spell, and he can do it several times each day - if successful, it is more effective at quickly ending a combat than a fighter or wizard.
My point - you don't need to have the classes be equal to be effective.