As much as I loved that first dog book I owned (sans GSP), it really lacked detail. Gorgeous pics and basic info, probably great for identification and a starting point... but not much deeper.
I love reading breed histories and I also really enjoy trivial facts like what famous people owned such and such a breed. :lol-sign:
I also really love hearing about temperament and personality and the ideal lifestyle for a breed, possible activities to do with your dog etc.
Edit - I know you asked for breeds... Other than the GSP that I keep going on about, I'd love to see the Tibetan Terrier! Although I'm pretty sure they would be a standard inclusion anyway. I love some of the rarer and regional breeds, the Gundog group seems to have so many breeds that haven't seemed to have found popularity elsewhere (well at least in Australia, it may be different elsewhere.)