Log files are not fun to look at. They are ugly, contain too much information, and often lead to massive headaches. Fortunately, these beasts can be tamed for more capacities than just debugging; they can used to generate wonderful reports that make sense.
Tools:
1. AWStats
2. Analog
3. WebTrends
4. Summary
5. Webalizer
Links:
WebServer LogAnalysis Tools Overview - http://www.serverwatch.com/tutorials/article.php/3518061
Analyzing Web Logs with AWStats -
http://www.onlamp.com/pub/a/onlamp/2005/12/01/awstats.html
Web Server Log Rotation and Analysis -
http://www.keithjbrown.co.uk/vworks/unix/logs.php