Warriors are warriors because they were strong, healthy children who learned that the best way to get ahead in life was through physical means. They weren't necessarily aggressive, but they knew that if you weren't at least strong enough to put up a fight, then somebody could kill you or worse. Since they spend so much of their time fighting, training, or practicing, they've become stronger and tougher. Alternately, they could just have natural strength and practice being large and in charge the same way a moose practises having antlers.
Wizards, on the other hand, may have come from more educated families. They could have always been more intellectual, more cerebral than their more brutish counterparts. They had learned from an early age that outsmarting your foes is easier and more useful than bludgeoning them to death. Since they spend their days using, practicing and learning magic, they're a little more intelligent than their sword-swinging cohorts.
But I digress.
My ideal system would be, basically, similar to the GURPS system, in that there would be only a couple of stats and then a couple more "derived" stats related to them. For example, Strength would have Fatigue as a derived stat, and Intelligence would have mana.
And here, I would like to digress again. As much as I love Vancian magic, and as much as I enjoy the writings, settings, and ideas of the man, I dislike the way D&D has dealt with Vancian magic. The magic, as far as I recall, was basically that magic was advanced mathematics and that the spell itself was torn from your head after you cast it. You would have to sit down and re-study the magic formulae after each casting, so alien was magic.
I don't want to get into some sort of wierd debate, so I'll just let it be said that it doesn't fit the flavour of the setting I have in mind. In this world, magic isn't a bizarre mathematical formula, and it isn't available to everybody. I'm thinking more of a Moorcockian magic, where magic is bought from otherworldly beings, with pacts and bargains and bloodlines figuring in more than one's ability to wave carved sticks.
Anyways, I'm thinking maybe a couple of stats.
One for your character's toughness; this one isn't debatable. Although I like systems where your health is more or less the human average, I like the idea of there being Herculean demi-gods alongside pale, sickly, and wretched peons or what-have-you. I'm thinking of just calling it Toughness.
There should be one for your character's strength. Again, this isn't really an option. I'll probably just call it Strength, although I like the poetry of calling it Might. There's something poetic about the stat being an examplar instead of a mere description, if that makes any sense. This is obviously more useful for the brutish warriors.
For an example, Brilliance. It's not called IQ, for Pete's sake. It's not a measured calculation of whatever, exactly, IQ tests are supposed to measure. It's a measure of how Brilliant you are. How much of an incredible genius. This would be useful for wizardly types.
Not really an example, but Dexterity. You should know what this one is.
The last stat would be Cunning. It's a measure of your character's deviousness, his responsiveness, and such. It's also a measure of his perception. It's more useful for wizards than warriors, but like all stats, should have a little something for everybody.
That gives us, in all, five stats: Toughness, Might, Brilliance, Dexterity, and Cunning. One for everybody, two for warriors, and two for wizards.