I'm not always enthused by the various Who spinoff publications, BBC or otherwise, but this one is a real winner (and I should say that in general I've been more than satisfied with Steve Tribe's work). Here we have the TARDIS examined from all angles, its non-fictional inspiration in the drafts of C.E. "Bunny" Webber, the designs of Peter Brachacki and his successors, and the various ways it has been used in the show, from both in-universe and external perspectives. It was published in 2010, just nicely in time for The Doctor's Wife the following year. It's fully but not obsessively detailed and gorgeously illustrated. I'm sorry I missed it on first publication (actually got it at a remaindered books fair in March). Here's a nice video review by someone else. You can get it here.