More online sources of free full texts:
Corpus Sciptorum Latinorum
Internet Classics Archive
LacusCurtis: Into the Roman World
Online Medieval and Classical Library
Perseus Digital Library
(in Latin only): Latin Library
Luminarium: Anthology of English Literature provides links to full-text scans and secondary literature about the writers.
and, at Infomotions, the Alex Catalogue of Electronic Texts
Infomotions features a Great Books Survey specifically concerning the Adler/ Hutchins Greats Books of the Western World set (and more specific still, the original 1952 version of that set, not the larger 1990 second edition).