Common Log Format

Windows (Extended) Log Format

A Handy Guide to Log Analyzers

Log Analysis Programs

Commercial Log Analyzers (The best there is, but expensive)

WebTrends - 30 day demo

HitList - 15 day demo of either Standard or Pro version (Free basic version)

Analog - Free, multiplatform

Webtrak - Cheap

SurfReport - very expensive
 
Sawmill - demo available, inexpensive