Some classical philosophers who were popular among Renaissance humanists had never been lost in the first place. Aristotle, in particular, fits into this category. Aristotle was influential among the medieval Scholastics, and he remained so duing the Renaissance, especially in the writings of Pico Della Mirandola.
Plato also occupied a significant place in Mirandola's thought, although his works are generally considered to be contrary to those of Aristotle. In fact, such was the popularity of Plato among humanists that Cosimo di Medici actually funded an attempt to reconstruct Plato's Academy in Florence, where scholars would study not just Plato, but his followers in the Hellenistic World, such as Plotinus. Over time, Plato's influence won out, and a major theme in the intellectual history of the Renaissance was the return of Platonism at the expense of Aristotle.
Another classical philosopher whose works were widely studied was Epicurus, whose philosophy emphasized pleasure as an important motive for human behavior. Humanist Lorenzo Valla, in his essay "On Pleasure," began by arguing that "pleasure is the only good." Erasmus was also an admirer of Epicurus. Machiavelli, who was a strong anti-Platonist in his political outlook, was influenced by classical Roman republican writers, in particular Sallust and Titus Livy.