Two potential lists, the inclusion of which is still uncertain, take the form of series of books published by Easton Press and the Franklin Library. The former's 100 Greatest Books Ever Written is the most obvious of three of its series we could use to make a larger list, the others being the awkwardly-titled Collector's Library of Famous Editions and the Books That Changed the World. The Franklin Library also has three series that would warrant inclusion: 100 Greatest Books of All Time; World's Best Loved Books; and Greatest Books of the World's Greatest Writers.
The problem with including the lists of these two publishers is that two other classics-publishing companies, of greater stature and showing stronger editorial control over their choice of books, do not offer, at least for now, potential lists for this project--precisely because they have been around longer than the leatherbound-book publishing companies (documented at Leather Bound Treasure). That is, for Penguin Classics and Oxford World's Classics, the two biggest names in this business, a complete list of said classics is not available; we know what's currently available, but further research would be necessary to find how many, or if any, previous Penguin Classics and World's Classics are no longer in print. The inclusion of books in the other series listed below, though a complete list of their classics is easier to construct, would thus cause an inconsistency in the project. A similar lack of information, and desire for inconsistency, is also why I am only including the final versions of lists that have gone through revisions: because, as noted previously, I do not have access to all of the editions of the Good Reading series.
Bantam Classics (now part of Modern Library)
Barnes and Nobles Classics
Classics Club (no longer extant, but here's a page at the Bookman's Answer)
Dorset Classic Reprints
Dover Publications Thrift Editions
Everyman's Library (currently under Random House)
Farrar, Strauss and Giroux Classics does not have its own page; nor does Harper Perennial Modern Classics
I Tatti Renaissance Library (produced by Villa I Tatti: The Harvard University Center for Italian Renaissance Studies, published by Harvard University Press)
Library of America
Loeb Classical Library (now part of Harvard University Press)
Norton Critical Editions
Oxford World's Classics
Penguin Classics, including its Complete Annotated Listing from a few years back (also of note is the Penguin Archive Project at the University of Bristol); also the Viking Critical Library, comparatively a short list, is part of the Penguin operation now--unfortunately, does not have its own page on their site; as is Signet Classics--previously all Signet series were part of New American Library, as was the varied Mentor series, which mostly consisted of non-fiction
Shambhala Publications has both Classics and Pocket Classics imprints
Simon and Schuster Enriched Classics
Tuttle Publishing has information about its Classics titles mixed in with others in its Literature category
There's some information here and there about Airmont Classics, which seem to be appreciated only for their covers
The Folio Society, like the "leatherbound" publishers, presents fancy versions of the classics, though with an emphasis on illustrations. Its predecessor of sorts, Golden Cockerel Press, is no longer extant, but the page at the site, Books and Writers, provides some details.
of these series serve a function similar to Robert Kanigel's book or
Michael Dirda's Classics for Pleasure: that is, they include works not commonly ranked as great or
classic, or perhaps that once were but have not received as much attention in recent decades.
New York Review Books Classics
Serpent's Tail Classics
Also, an older series, Sacred Books of the East, has a Wikipedia page with links to full-text scans available at the Internet Sacred Text Archive and elsewhere.