There are a few good books, not exactly Irrlicht-centric, but covering advanced 3D mathematics topics that would help you "pimp your irrlicht" to the fullest.
Any kind of 3D math primer would be helpful, but I don't think there is a book specific for Irrlicht development. Why not? Who knows, it certainly deserves one. Ogre got one a few months back and it looked pretty detailed and helpful (I believe it was just some random member on their forums who decided to get it published.) So its not unheard of for an indie engine to get its own book.
'Game Coding complete' by Mick McShaffery was a good book. It looked into good coding practice and had code like 'making your own scene graph' and a very useful smart pointer class that deallocates itself . It then goes into managing/producing a game.
BTW: also has a simple primer on Vector and Matrix math... and I think the 2nd edition has networking and physics