First and foremost of course there is Ansel Adams. His three book set (the Camera, the Negative, the Print) have been on my bookshelf for many years, and long before I got into digital photography. His 40 examples book is a great classic that I should buy someday. I am sure there has to be Ansel Adams sites and information out on the internet, but you can do the Google search to find them.
Galen Rowell has done a lot of great photography, and written some very worthwhile books. He is indeed from the film era, but there is plenty to learn from any great photographer, so that shouldn't keep you from his books. The first that comes to mind is Mountain Light, but there is also a book Galen Rowell's vision that seems to be a collection of articles previously published in the Outdoor Photographer Magazine. Galen and his wife Barbara died just a few years ago (August, 2002) in a tragic small plane crash near Bishop, California. Galen was 62 years old, his wife Barbara was 54.
The Mountain Light website is thankfully still online, and you can look at a collection of Galen Rowell's articles, as well as a very interesting rundown of the gear he used.
One of the articles in the "vision" book also gave a List of Galen Rowell's gear. which I have found quite instructive. In particular I note that the 24mm prime lens on his Nikon is his all time favorite lens. (The 28mm on my Pentax was my all time favorite, and I always itched to have a 24mm).
Another fellow who has taken some fine photographs and written some very worthwhile books is John Shaw. He has written a LOT of books, but the one I have seen and enjoyed is John Shaw's Nature Photography. Interestingly, in his discussion of wide angle lenses, he also favors the 24mm, but says if you have a 28mm, don't loose any sleep, move back a few feet and reframe your subject and instead of buying a 24mm lens, spend the money you save on a good tripod. How did he know about my quandry?
Some other superb photographers:
I really liked The National Geographic Photography Field Guide, anyone who hasn't taken note of the excellent photography in National Geographic just isn't paying attention.
Complete Digital Photography by Ben Long (now in it's third edition) was quite worthwhile, as is the web site.
A somewhat unusual book I just happened to trip across is The Backpackers Photography Handbook by Charles Campbell. This one is from the film era (1994) and the man uses Nikon equipment. He introduces his Chroma-Zone exposure system which is based on a +-2.5 stop range on slide film.
A book called Shooting Digital has a good review.
Another one (I haven't seen this yet) is: digital secrets
I used to have a bunch of small books from Kodak, such as How to Take Good Pictures (and something by this title is still available from amazon.com).
Another one that sounds good is the book Photoshop for Photographers.
In a local used bookstore I ran across this little marvel: EOS Lens Work III. It is done by Canon and is a beautiful hardcover book, circa 2003 featuring the Canon EOS lenses (omits the latest EFS lenses such as the 60mm macro and the 10-22mm ultra wide zoom). It seems to be out of print, and I have mixed feelings about spending money on what seems to be a product brochure on a grand scale, but it is a unique resource.
Uncle Tom's Digital Photography Info / tom@mmto.org