We have these beings called Rakshasas on Ravana's side and monkeys and bears on Rama's side. I don't recall reading about any humans beside Rama and Lakshmana fighting on either side. For that matter, its not clear if Rama and Lakshmana ran into any humans after the abduction of Sita until they came back to Ayodhya.
Rama and Lakshmana are the only two humans who fought the war. No humans besides Rama and Lakshmana fought the war in human form. Vibhishana and his companions fought the war in the guise of humans.
It was a war strategy not to change the forms of Vanaras as a form of recognition among the vanaras.
Only seven fought the war in human form. (Thanks @TriyugiNarayanMani) They are
- Vibhishana and his four companions.
Monkeys should not assume human form in the battle, for, in the army of monkeys, this monkey-shape should serve as a sign of recognition among us. Among our own people also, the form of monkeys will become a sign of recognition for us. Seven of us will attack the foe in our human form, I, my brother Lakshmana, who is full of valour, my friend Vibhishana and his four companions.
Rama mentions Vibhishana and his companions as fighting in human form because Rakshasas are able to change their form by their will.
They met humans after the abduction of Sita. It is known from Ramayana. They met Shabari at the hermitage of Matanga.
On getting at that hermitage and on perusing at that picturesque environ that is wreathed round with several picturesque trees, those two came nigh of Shabari. On seeing them that sublimated yogi Shabari instinctively made palm-fold, got up imperatively, and then she braced the feet of Rama, and even that of sagacious Lakshmana, impressively.
In Valmiki Ramayana she is only said as a sublimant yogi and an ardent devotee of Rama but in later versions of Ramayana like Ranganatha Ramayana (Telugu) and Odia Ramyana, she is depicted to have utmost devotion towards him and offered fruits to Rama and Lakshmana. She tastes berries whether they are tasty enough and then gives tasty ones to Rama in Odia Ramayana.
Rama also met Sage Agastya (he is born of a pot and common son of devatas Mitra and Varuna though). He is the one who said Aditya Hridaya stotram to Rama for gaining victory over Ravana.