I thought we were discussing significant authors who did not use DRM, not ones who sometimes gave out free promo stuff?
In any case, here's one who kind of fits both categories:
Peter Watts is a Canadian science fiction author who won the Hugo Award for 2010 and was again a Hugo finalist for 2011. He is published in English by Tor/Macmillan, and no doubt his Tor/Macmillan books are DRMed.
However, he offers everything of his free and DRM-free under a Creative Commons license
on his website, where you can download the lot.
Everything. Even the Tor-published still-in-print-and-reprinted-in-new-rerelease-paper-editions-as-well novels. The only thing which seems to be "missing" is a short story which can be read free online over at the Clarkesworld magazine site anyway.
He's been doing this for a number of years now and has yet to be driven to starvation or relocation into the gutter by non-paying downloaders reading him out of house and home, and he is currently in the process of writing another novel for Tor/Macmillan.
(Not that either of those would be likely to happen anyway, since Canada has fairly decent social safety nets, not to mention arts grants and gives out a small amount every year to Canadian authors who have their works on public library bookshelves, every single one of which in my area carries Watts' novels.)
People
regularly drop money into his Paypal tipjar as thanks for the freebie e-books, and it seems that it's just in recent years since he started offering the website downloads that he's become prominent and known enough to get the award nominations (which tend to ignore most Canadians, Robert J. Sawyer being a noticeable exception).
He's even available in official translation into French, which is how I mainly buy his works (although I do have some hardcovers and paperbacks of a few of his print editions), which I can tell you is actually relatively rare for English-language speculative fiction, and generally only the most popular/classic/prominent works get that particular nod from the Francophone sf/fantasy lines.
So, neither being DRM-free, nor offering the entirety of his work free to download online seems to have damaged Peter Watts' earning abilities or standard of living, even after the medical bills and whatnot he has from having flesh-eating bacteria in one leg, and in fact seems to have raised his profile and contributed to his publicity, and likely sales as well.
(It's also only been in recent months that his long-standing older novels have become available in French translation, whereas his newest was translated fairly shortly relative to publication after his Hugo win. Francophone imprints seem to be very picky about buying the rights for older backlist title vs getting just the hot new bestsellers from a temporarily "star" author.)