Patrologia Graeca (ed. Migne)

The standard collection of Greek Christian texts, in 161 volumes. Edited in the late 19th century by Migne. These are not critical editions.

http://graeca.patristica.net/

http://www.documentacatholicaomnia.eu/a_1010_Conspectus_Omnium_Rerum_Alphabeticus_Littera_A.html