Kumudvati, Chief Queen of Kusha (son of Shri Ram) was a Naga Princess of Sarayu river and her father was killed by Garuda. Naga King Kumud offered her to Kusha in peace alliance when Kusha had almost annihilated the Nagas when Kumudvati took his golden arm- bracelet mistakenly. Kusha married her and she gave birth to his eight sons and a daughter named Champakmalini. Her son Atithi was heir to the throne and when Kusha died, Kumudvati followed him in death like moonshine follows the moon. Her mention is in Raghuvansh and Ananda Ramayana not in Valmiki Ramayana. She was really beautiful, timid and shy and was a young maiden (kanya) when she married Kusha. Kusha had built Nageshwarnath Temple for her near Sarayu river so that she could worship Lord Shiva.
Champika
Champika was the first wife of Kusha and she had chosen Kusha as her husband in her Swayamvara. She was daughter of Maharaja Bhurikirti, King of the lands East of Ayodhya. Rishi Agastya prophesized about her to Shri Ram that she won't be having any sons but daughters. She eventually gave nine daughters to Kusha and their eldest daughter Hema was married to Prince Chitrangad of Avanti after her Swayamvara and a war after which Chitrangad and his son father Ugrabahu were pardoned by Shri Ram. Her reaction to her husband's marriage with Kumudvati is not mentioned but she seems like to enjoy her previous status as the seniormost Queen (Pattmahishi) despite Kumudvati being Chief Queen (Agramahishi or Mahadevi). She was respected in the royal house. Her sister Sumati was married to Kusha’s twin brother Lava.
Kumbhinasi
Kumbhinasi was daughter of Anala, Kaikesi’s younger sister and Vishvavasu. When she was staying in Antahpura of Ravana in Lanka and she was protected as a sister and enjoyed luxuries but she was daringly abducted by a demon named Madhu when others were not around in the palace. When Ravana got to know about this, he got really angry despite himself abducting many women. He went with his warriors to Madhura (Mathura) to kill him but Kumbhinasi pleaded him to not kill her husband. Then Ravana pardoned Madhu and made him his ally. She was mother of Lavanasura who later was defeated by Shatrughna. Shatrughna named the city Surasena after conquering it and the same land became the birth place of Shri Krishna years later.
There are many other characters in Valmiki Ramayana and other renditions which are lesser known like Mahaparshva, Sushena, Vidyutjhiva (husband of Surpankha), Prahasta, Kabandha, Yupaketu (son of Shatrughna in Ananda Ramayana) , Madansundari (princess of Shivkantipuri with whom Yupaketu did Rakshasa Vivah), Kanjanayana (Naga Princess whom Lava married) , etc.