I realize that Loebolus sounds like a rather bad SyFy channel horror movie, maybe something about a zombie classics scholar terrorizing Harvard. Loebolus is actually a very cool project from Ryan Baumann which collects all 277 of the downloadable Loeb Classics on a single page. You can download any individual volume or the whole set in a single 3.2 GB file. In May 2022 Ryan updated the page a little, and I have updated this post (Originally published in 2012!)
Ed Donnelly has most of this information on his dosnLOEBables site, along with links to ABE or Amazon to purchase the actual books. But Loebolus gets you directly to the PDF without entering captcha codes. I downloaded two files as a trial, both were scanned so that each page is a separate image, Greek and English alternate. I sent Josephus’ Life to my Kindle App on my iPad for easy reading.
This is a goldmine of Classical texts in Greek and Latin, all now in the Public Domain. All of these books are available from a variety of sources, including Logos (See my comments on the Perseus Collection from Logos here) and archive.org.But I find Loebolus to be a very elegant, simple site to use that has exactly what I want.
For biblical studies, the works of Josephus are available. While I realize that Josephus is commonly reprinted, these PDF files will also give you the Greek text and an abundance of information via footnotes. Strabo’s Geography, Herodotus, Xenophon, Plutarch are all there. I am also fond of Thucydides, Peloponnesian War (all four volumes are available).
The Loeb Library is a collection of Greek and Latin classical sources. These small books have the Greek or Latin on the left side, and an English translation on the right. Some of the volumes have been replaced with newer translations. Marital, for example, was recently replaced with a modern, vulgar translation, which more accurately reflects Marital’s original shocking language. (Marital was something of the Lenny Bruce of his day). For many of these books the only English translation available is the Loeb version. I am not sure we need a fresh translation of Theophrastus’ Enquiry into Plants, but other important historical texts have been updated.
Whether you download the whole set or just pick a few of the best, Loebolus is worth checking out.