You will find permanent links to reference texts at the bottom of each page of the Prabhupadavani website.   There are the three main scriptures: Bhagavad-gita as it is, Srimad-Bhagavatam, Caitanya-caritamrta.  And also,  the Science of Self-Realization, Srila Prabhupada Lilamrta and Srila Prabhupada Uvaca.  These books are hosted by the Bhaktivedanta Vedabase Online.