Without magic, D&D falls apart. You'd have to re-work most of the Monster Manual, exponentially reducing CR as the numbers exploded (as they oft do in 3e).
Psions would kick ass, as would ardents. (Well, they already do, but they would do so eve more.) Soulknives would stop sucking and become not-crap. Psychic warriors would still own them, of course, but that's not important.
Incarnum classes would work, I think. I mean, the faux-paladin they have is still weak, but it can meldshape, so whatever.
...And that's about all I care to contribute, since I should be in bed.
No, Soulknife would still suck. Rogues beat soulknives so bad it isn't funny.
Erudite, as the only Tier 1 classes, probably becomes nerfworthy; if spells don't work, I'd say Spell to Power doesn't either. Psions and supplemented Binders are Tier 2 though this tier is fairly thinned out. Ardents don't really change that much; they're fairly Tier 3 thanks to their restricted lists. The real thing in favour of Ardents is their lack of a maximum power level known in gish and dual-caster builds.
Also, you would as often as not need to *lower* monster CRs; most monsters are statted without gear, and have little to no actual spellcasting abilities. Dragons get heavily nerfed, but the Crystal, Planar and Incarnum dragons all work fine.
In terms of maink the world work, Psionics is the most likely base magic system, though the others would be used where they are stronger. Binders with Buer, possibly teamed with Incarnates, would take up healing, Shadowcasters could do the Beguiler-ish, Necromancer-ish stuff they wanted to all along, Totemists and Psywars become viable gishes without the cleric overshining them, and all the non-magical classes get their moment in the sun with the Tier 1 canopy removed.
Certain things become more and more lacking; there is very little magical ability to create/improve food without magic, so the world is likely to be more agrarian. Also, psionics is less effective at big, splashy effects, so mass warfare becomes less useless. Finally, without a power source that responds only to worship or dedicated study, bards, rogues and experts rise to fill most of the social power roles, where their skils can come to the fore. Incarnates and Psions will take a few of these roles, but psions are less history-oriented than wizards, giving bards a bit of breathing space, and incarnates tend to have bigger things on their minds than running cities (unless they're Lawful, that is...).
