Perhaps something like mages from Vance's "Dying Earth". They are actually not very like D20 wizards. They more resemble fighters or rogues, fighting with swords, but without armor and with a few per day powerful spells. (actually, their spells were not per day, but they could as well be - their spell-books were not portable).
I would also think about Elric of Melnibone - swordfighter who buffs himself with magic, with good summoning spells; Zelazny's Dilvish the Damned - also swordfighter, but with a city-killing spell.
eg something like:
BAB - as rogue
fairly high skills
at will-magic armor, shield, cantrips, eventually some buffs (blur etc)
per encounter- true strike, various touch spells (Shocking Grasp etc), eventually some non-damaging spells (like expeditious retreat, jump, etc), some illusions and pyrotechnics (in the general sense) to confuse foes
per day - like wizards
Not proficent with armor. Cannot use his abilities when wearing armor.