I personally like Leather Armor and Toughness. However, of those two, only Leather Armor is a no-brainer.
For your At-Will powers, a human wizard has some great options. With the addition of Arcane Power (or Dragon Magazine), he can pick one At-Will power for each of FRW, and thereby maximize his chance to hit any given foe.
I agree about swapping out Ray of Frost -- it's a power I dislike, since Thunderwave hits the same defense, and does more. My dude enjoys using Thunderwave.
Scorching Burst is a great power. It targets Reflex.
Magic Missile is great if you expect to be fighting at long range (11 to 20 squares). Do you have an Archery Ranger, a crossbow Rogue, and an archer Bard? If so, take this power. If not, it's redundant with Scorching Burst.
My favorite At-Will power that targets Will defense is Illusory Ambush (from Arcane Power and also printed in Dragon). It is single-target, but the rider effect is nice.
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For your Daily powers, I'd strongly recommend trading out Sleep and using Flaming Sphere instead. The only Wizard who should be using Sleep is a Paragon-tier Orb wielder, and even he shouldn't really use it (because in his hands it's too strong).
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My favorite Utility 2 power is Shield. It's saved my PC's butt more times than I'd like to remember.
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Fire Shroud is a fine Encounter 3 power. It goes very nicely with an Orb-Wizard, since it's your earliest "save ends" Encounter power.
Cheers, -- N