A distributed logging & monitoring WS architecture using WS-Notification (WSN) as well as a Log4J appender that implements an appropriate adapter. Software components that already use Log4J can be integrated non-intrusively.
LogCrawler is an ANT task for automatic testing of web applications. Using a HTTP crawler it visits all pages of a website and checks the server logfiles for errors. Use it as a "smoketest" with your CI system like CruiseControl.