Before I get to the books, there a a couple of other resources you should consider. In my opinion, every Disney park history fan should subscribe to E-Ticket Magazine. Its a small, quarterly magazine that contains some of the the most thoroughly written and well researched articles on Disney attractions available anywhere. Back issues are also available, some in print form, some on CD Rom. Here is a link to their site:
http://www.the-e-ticket.com/
Also, be sure to check out Bob Gurr's web column, Designer Times. Bob was one of the orignal Imagineers. He designed the Omnimover (best known as the Doom Buggy in the Haunted Mansion), the first monorails, the Autopia cars and just about everything else that moved in the parks. He has been writing the column monthly since May of 2000, so there is a lot to read. Here is a link to a list of all his columns (I suggest you start from the bottom of the list and work your way to the top) :
http://www.laughingplace.com/News-Previous-C-GURR.asp
There are several good books out there, though some are a bit pricey.
Far and away the best book on Disney park history is "The Nickle Tour" by two imagineers, Bruce Gordan and David Mumford (who died last year). This book looks at each attraction from
Disneyland's opening day till approx 4 years ago and contains more information and inside stories than any other book I have seen . It also contains a picture of just about every postcard ever sold at Disneyland. If you buy no other book on the Disney parks this is the one to own.
Amazon has it.
"Walt Disney Imagineering", written by the Imagineers, is a great overview into the imagineering process. It also contains some great photos of models and prototype used in designing attractions. I found the sections on Temple of the Forbidden Eye, Tower of Terror and Epcot to be particularly interesting. Amazon has it.
"Designing Disney: Imagineering and the Art of the Show" by John Hench (one of the original Imagineers) is a new book that talks a great deal about the Imagineering process. I just got my copy, so I haven't gotten to far into it, but I like what I have seen so far. Again, Amazon has it.
"Designing Disney's Theme Parks : The Architecture of Reassurance" is another very good book about the process of designing a Disney park. The book was originally a companion piece to an amazing travelling museum exhibition (I spent six hour in Dallas mesmorized by the exhibition) which has since ended its tour. Amazon has this one too.
On last place I recommend with a bit of a reservation. At one time, the premier Disney history mag was Persistance of Vision. These were incredibly well done mags (each was almost a book in itself. usually around 100 pages). However, 3 years ago, the editor just stopped publishing (always promising the next issue would be ready in "6 months"). I DO NOT recommend that you subscribe to this magazine, as I you will most likely never receive anything for your money. However, back issues are available. I highly recommend the Worlds Fair issue (double issue #6/7) and the Haunted Mansion issue (issue #9). I would contact Paul Anderson, the editor of PoV, before ordering however to be sure these issues are still available. Here is a link to the PoV wab site back issues page:
http://www.disneypov.com/backissue.html
That should be enough to keep you busy for awhile. Please feel free to PM me if you have any questions.