I recently discovered a sight that reproduces Migne’s Patrologia Graeca for free as PDFs. For my NT and other readers, this is the standard compilation of the Greek patristic works through the 15th century. This isn’t the critical edition of all these texts by any means, but it is the easiest place to look up and find things since almost all academic quotations list the PG reference.
Note: The web site is all in Greek.
Thanks Kevin for passing along such a great site!