Bhagavad-Gita (Popularity: )
http://www.bhagavad-gita.org/ Text and audio recitations in many languages, along with a description of the Brahma-Madhva-Gaudiya sampradaya and avataras of Krishna.
Valmiki Ramayana (Popularity: )
http://www.valmikiramayan.net/ The epic poem by Valmiki Maharshi of Lord Ramachandra's war with the evil demon Ravana. Original Sanskrit and English translations.