www.baen.com - They have a Free Library and a storefront that sells individual books at sub-paperback prices (DRM-free) as well as selling monthly bundles (called webscriptions) of 6-7 books for US$15. DRM-free, again, in your choice of formats.
http://baencd.thefifthimperium.com/ - collects BAEN's promo CDs with dozens of legally free ebooks each.
Mobileread:
https://www.mobileread.com/forums/ebo...&sort=dateline
Munsey's.com - tens of thousands of pre-1923 books. Or you could search for "Exquisite Enigma" at ebay and get 25,000+ ePubs on two DVDs for US$7.98 or so.