AWStats is a powerful, free web log analysis tool. I had a client that had some specific reporting needs–parsing urls retrieved and reporting how many times any document in a specific set of directories (but no other ones) had been viewed.
Luckily, AWStats is configurable enough to do this using the Extra Sections feature; in fact, there is an example in the documentation showing how to do exactly what the client needed. In fact, you can do a ton with regular expressions and AWStats. Basically, if the data is in the web logs, you can build a custom report for it.