Not productivity related, but the most important thing IMO that an office should have is a view of the outside. It is more than just something nice to look at. If you spend as much time as I do in front of your monitor(s) you need to regularly focus on something in the middle to far distance to reduce eye-strain. I've done a quick search on the internets to find this:
http://www.pasadenaeye.com/faq/faq08/faq08_text.htmlI've no idea if this is scientifically proven or anything, but looking away from the monitor every once in a while can't be bad for you.