Gowland is one of the giants. His books are also well worth reading.
By the way, here's the book I couldn't remember the name of:
Bernard of Hollywood's Ultimate Pin-Up Book by Bruno and Susan Bernard
9x12, 360 page, more than 450 pics. A tour-de-force of the Golden Age of Hollywood. Hey, so it's $42.50 - that's less than ten cents a photo! [img]/ubbthreads/images/graemlins/smile.gif[/img]
You can also see Bernard's work in this smaller collection:
Bernard Pin-up Book Set
This is three little hardbound books, called "Brunettes," "Blondes," and "Redheads" respectively, with each concentrating on women with the sort of hair referred to. Each has 25 vintage Bernard pics and an intro from Susan Bernard. At six bucks for all three (the cover price is $6.95 *each*) they're a steal.
Bud Plant Comic Art has a large and ever-changing variety of books on pin-up, nude, and erotic photography, and I recommend them highly. Their service and merchandise are topnotch.