Books I use most: Cote, Fossum, and Plumbs (even though it's on VIN, I find myself grabbing the book). I doublecheck myself with Plunkett (Emergency Procedures for the SA Vet) frequently, but it's not necessary for a new GP. Also for critical care, SA Crit Care Medicine by Silverstein is awesome. For exotics, the pink book "Ferrets, Rabbits, and Rodents" by ... uh ... Quesenberry and Carpenter?
There is probably another 10-15 books I reference once/month or so, but all our hospitals have a fairly reasonable library so I don't purchase any of them.