"Don't look at the print date - it is still the best source on IOS security/firewall features that it covers. Take note that it doesn't include new features like Zone-based firewall,Control Plane defenses and other things relevant to new IOSes."
"THE ASA/FWSM handbook, the closest to the source thing you can get with examples/explanations/experience tidbits. Hucaby was one of the beta-testers of ASA/PIX 7.x/8.x firmware. Be aware it does not include VPN topics ."
"The author of the Cisco Router Firewall Security does the great job again. Everything VPN-related, except SSL VPN (it does have chapter on it but rather sketchy). A must for anyone doing VPNs with Cisco gear."