I love to read. I especially like to read about stamps. I subscribe to many philatelic publications. I get questions from readers about good books to read. Here is a list of books that I enjoy:
The introductory pages of the Scott US Specialized catalog. There is a wealth of knowledge about watermarks, perforations, printing methods, and so forth. You would be surprised how many questions I get that could be easily answered by reading the front of the catalog.
Any book by Herman "Pat" Herst. Pat is one of my favorite philatelic writers. His book Fun & Profit in Stamp Collecting tries to explain the stamp market in plain English like I did here today. His other books are great reading and often times humorous. I own and read every book that Pat wrote about stamps. I've read all of them at least twice now.
The American Philatelic Congress Books are full of original research. Although not devoted to strictly US stamps, there is usually at least one article about US philately in every Congress book. It's great reading on topics you won't find in Linn's, the American Philatelist, etc.
The Dealers' Guide to Chemical Restoration of Postage Stamps. It's a little dated, but it's still a good book on how people try to fake stamps. On a similar note, How to Detect Damaged, Altered and Repaired Stamps by Paul W. Schmid is a great book too. Here's a clue. Watermark fluid is useful for much more than just finding watermarks.
The Micarelli Identification Guide to U.S. Stamps, Regular Issues 1847-1934 by Charles N. Micarelli. A good book with lots of information on how to identify early US stamps. The charts are easy to use and help quickly identify your stamps. It's a condensed checklist of what to look for to identify stamps. It's much easier to use than paging through the Scott catalog. I use my copy a lot. It saves me a lot of time.
Any of the Opinions books from the Philatelic Foundation (there are now 7 volumes). This is great information on how the experts go about evaluating items for certificates. It's great insight into what makes an item good or bad. It's like a detective story on philatelic items.
Those are some of the books that I use often or I read them over and over again. If you like to read, they are worth your consideration.