I found this awesome article in the last two issues of BSD Magazine (August and September 2010) on setting up OpenBSD for network monitoring. It appears to be a reprint of an article from Kernel Panic. This will probably be my next major project.

http://www.kernel-panic.it/openbsd/nagios/

If you’ve never checked out Kernel Panic they have some really useful articles on OpenBSD, Linux, security, programming, etc.