OSSEC 1.5, a popular open-source intrusion detection system (IDS), is now available. The new version introduces support for Checkpoint, Smart Defense, and Shorewall logs, as well as Postfix and Asterisk logs, among several other new features.

If you haven't tried OSSEC then consider doing so. It runs on Linux, UNIX (OS X and BSD), Windows, and Solaris, and offers "a correlation and analysis engine, log analysis, file integrity checking, Windows registry monitoring, centralized policy enforcement, rootkit detection, real-time alerting and active response."

Oh, and it's free!