Dedicated server monitoring tools have largely replaced the need to manually parse log files except for the most esoteric of issues. This however raises another issue — selecting one that has the right combination of features, usability and performance. Fortunately, many free options exist if you're willing to learn their ins and outs.
Chetan R over at Six Revisions has put together a list of the better candidates — ten to be exact — ranging from the slick, well-presented Performance Co-Pilot, which has a history going all the way back to Silicon Graphics, to the more straight-forward presentation of Monit from Tildeslash.
While the Six Revision's post doesn't go into extensive detail about each option, it should give you a good starting point for your own investigation.
Considering some are easier to set up than others and a few have certain platform requirements, your best bet is to try a few out to figure out which one is ideal for your server configuration.
10 Free Server Monitoring Tools [Six Revisions]