DenyHosts is an application that inspects syslog and adds hosts to /etc/hosts.deny after a configurable number of failed logins. I started using it exactly a month ago, and it has so far denied 60 hosts that attempted to connect with ssh. The logwatch filter just includes a section in the daily e-mail telling me what it added to the hosts.deny file.
Spamassassin stats are quite simple, but I wanted a quick overview of what the system was doing. It will include a section like this in the logwatch report:
x messages marked as spam
y messages marked clean
z total messages processed
x percent of mail was spam