Instant Photo Library...
The Life Library of Photography, published by Time-Life Books in the early 1970's, remains one of the best photography book series ever produced. I own the complete set, and consider it the core of my photography library. The production quality of these books is top notch; beautifully bound in a 10" X 10" square format, and the photography reproduction throughout is outstanding.
I use these continuously as a reference source as well as just for the pleasure of viewing classic photography.
If you are trying to build a photography library I would urge you to begin with any book from this series, and start collecting them. They come up on Ebay all the time, as well as used book stores. Typically five to ten dollars will get you a book in good condition. I keep an eye out for Ebay listings of the full set, and one came up today with a starting bid of $30. I have no connection to the seller, but they appear to have a high feedback rating. Take note of the shipping weight of the books in consideration of your bid if you are looking to buy these, but in my opinion, if you can get this set for $100 or so, you have made one of the best photo book investments you could possibly make.
Complete set of Life Library of Photography on Ebay