To start exploring this topic, here are some Storybooks about rakshasas from past semesters of this class. You might also want to review these articles at Wikipedia about rakshasas (the female rakshasas are called rakshasis), asuras, and daityas.
All the major demon characters also have their own articles at Wikipedia. There is Ravana, of course, and his family: Surpanakha, Kumbhakarna, Indrajit, etc. There are also other major demon characters in the Ramayama such as Viradha, Ilvala and Vatapi, Taraka/Tathaka and Maricha, along with Hidimba and Hidimbi and also Bakasura in the Mahabharata.
In addition, there are many famous demons who were defeated by the gods, such as Hiranyaksha, Hiranyakashipu, Holika, Mahishasura, Raktabija, and Vritra.
Although many of the rakshasas and asuras are evil creatures, this is not always the case, as characters like Vibhishana, Prahlada, Mahabali, Maya, and Ghatotkacha show.
The image below shows Ravana, ruler of Lanka and king of the rakshasas, as he battles the bird Jatayu: