I created a Pinboard dedicated to The Old Kingdom a few weeks ago. It's up for public viewing here. These are images I've found via DeviantArt, Tumblr, and Google Images. (If you see your own work on there and it isn't credited, let me know! I can add source links for every image.) If you've been wanting to give the books a re-read or just want to see what kind of wonderful artwork is out there, well, I've trawled the internet top to bottom!
All in all, though, I've noticed a severe lack of Nicholas Sayre. :( It's a shame. I don't think he's a minor role but actually rather pivotal in places! There's lots of unanswered questions about him going forth from The Creature in the Case!
- Images inspired by Garth Nix's Old Kingdom