Nobody has yet mentioned The Mythical Man Month by Fred Brooks (1975) which I must quote from at least monthly. Certainly much has changed since OS/360, but it is sometimes surprising to see how much has not changed.

Update: I was a bit surprised to see jdporter's list date this as 1972, but sure enough that is shown in my copy as Fred Brooks' own copyright date. Evidently it took him 3 years to get a publisher interested. The 20th anniversary edition was published in 1995 - I guess 23rd anniversary didn't have the same ring to it ;-)