I'm currently reading the "Linux Networking Cookbook", by Carla Schroder. I chose this book as I'm constantly working with networks, primarily with linux workstations and notebooks, Mac OS X desktops, as well as FreeBSD based (pfSense and m0n0wall) firewalls and routers.
While pfSense and m0n0wall make setting up a firewall and VPN pretty easy, I stil have many questions about routing, sub-netting and network architecture best practices. I hope by reading this book, I'll gain a better understanding of how "good" networks are built, and how to avoid potential problems with an uncertain future about how a network will evolve and be used.