Loeb Classical Library: Free Out-of-Copyright Downloads Online

The Loeb Classical Library is a series of books by Ancient Greek and Roman authors designed to make the text accessible to the broadest possible audience, presenting the original Greek or Latin on each left-hand leaf and a fairly literal translation on the facing page. As their early translations pass out of copyright many are available online for free, here: http://www.edonnelly.com/loebs.html
The Clay Sanskrit Library and I Tatti Renaissance Library both have facing page  translations.