Often counted as the first Neoplatonist, Plotinus' teacher, Ammonius Saccas of Alexandria, was, as one can judge from the (scarce) remains of his other students' teachings, really still a Middle Platonist. What I mean by this is that the important innovations we associate with Plotinus really are his own, and not those of his teacher. Still, Ammonius Saccas' role in philosophical history is an important one: almost every prominent Platonist of Plotinus' generation studied with him. However, their very entensive mutual disagreement, and the lopsided transmission (dominated by Plotinians), make it very difficult to reconstruct the nature of Ammonius' teachings.
Although the identity of Ammonius' student Origen, an important professor of philosophy, and the Christian Origen is highly implausible, it is still assumed, on the basis of Eusebius' testimony, that the Christian theologian-philosopher was also a student of Ammonius Saccas. I don't know whether this can be taken as fact, since Eusebius also confuses Ammonius Saccas with a Christian author. I suppose it is plausible enough, but I will not include him here.
See my page on Early Neoplatonism.
Origen "the Pagan"
Porphyry of Tyre
Student of Longinus and, later, of Plotinus; because not all of his works can be clearly assigned to either the Middle Platonic phase before studying with Plotinus, or the Neoplatonic phrase after he accepted his new teacher's doctrine, I treat everything together on my page on Early Neoplatonism.