Cisco Netranger
Cisco Netranger
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/netrangr/
Snort
The open source snort intrusion detection and prevention system is the most
flexible and widely deployed solution available.
http://www.snort.org/
Tripwire
Tripwire
http://www.tripwire.org/