I am sure many of you will appreciate Open Library (Open Library) as it contains many texts (some out of print) which can help in any type of study. I was able to find a very good condition scan of Taswell Langmead's "English Constitutional History" in almost all prints from 1858-1960. Very good read for those interested in English common law. But you can find nearly any philosophy, history, etc. book in the archive. It is done through the California State Library, so its not illegal or anything like that. They also have software available so that you can scan your copies of the texts they need. Just remember to check the scanned books box before you search otherwise you will sift through books that have not been scanned yet.

For example, I did a quick search for Cicero and came up with over 421 scanned copies. I have the Penguin collection of Cicero and matched most of them to these four specific copies (with the exception of the compilations by penguin i.e. On the Good LifeThe letters of Cicero
the whole extant correspondence in chronological order
by Cicero, Marcus Tullius.
Published in 1920, G. Bell and Sons (London)
Open Library: Details: lettersofcicero01ciceiala

The Republic of Cicero.
by Cicero, Marcus Tullius.
Published in 1829, G. & C. Carvill (New York)
Open Library: Details: republicofcicero00cicerich

Cicero on oratory and orators
with his letters to Quintus and Brutus
by Cicero, Marcus Tullius.
Published in 1896, G. Bell (London)
Cicero on oratory and orators (Open Library)

Ethical writings of Cicero
De officiis, De senectute, De amicitia, Scipio's dream
by Cicero, Marcus Tullius.
Published in 1887, Little, Brown (Boston)
Ethical writings of Cicero (Open Library)

But openlibrary also has very good copies of The Divine Comedy, Faust, Complete Works of Plato, etc. Enjoy!