I just added an essential tool to my toolset. Microsoft LogParser. This great tool allows running of SQL queries against a variety of log files and other data sources. Here's an example query
SELECT date, REVERSEDNS(c-ip) AS Client, COUNT(*) FROM IISLOG.log WHERE sc-status<>200 GROUP BY date, Client
The same can be ran against event logs, registry, csv, xml files, and much much more.
The link to Microsoft download site is: http://www.microsoft.com/downloads/details.aspx?FamilyID=890cd06b-abf8-4c25-91b2-f8d975cf8c07&displaylang=en
There is also a great helper site: www.logparser.com with a large collection of scripts to help with the more complicated admin tasks.