In terms of services, we use Nagios , which is an open source package similar to WhatsUp Gold. It comes with a bunch of stuff for common services, and we've written a few routines to handle particular apps, our Internet download limit etc.

For event logs, one of our contractors left us a script which rips through the event logs on a server nightly, ignores anything you've told it to expect and then sends an email with anything unusual. Unfortunately they consider it part of their service; I can't forward it.