Todd Klein, who is one of the best letterers to ever work in comics, is also a pretty good historian. He recently completed (I think) a series over on his blog about the various offices of DC Comics for which he's worked in his career. With a lot of help from others, he dug up photos, not just of the star writers and artists but of the other folks who made the comics come out — people in the art department, licensing, contracts, overseas sales, etc. Here are links to Part 1, Part 2, Part 3, Part 4, Part 5 and Part 6.
Todd's history starts in 1982 as DC moves from 75 Rockefeller Plaza to 666 Fifth Avenue. My own history with their offices started in 1970 when they were at 909 Third Avenue…in a building that seemed way too corporate and serious to have comic books produced within. Over the years, it seemed to me the various offices got more casual and fun, and the average age of an employee seemed to get younger and younger…though there were always longtime staffers around to tell you how it was in "the old days." I have (mostly) fond memories of visiting the various offices, hanging around and meeting people and sometimes conducting actual business.