A lot of good options have been mentioned. I think it's important to consider who the primary audience is. If you or another knowledgable Perl programmer are reading the logs, then I like Data::Dumper or some module that does a good job of showing exactly what the perl data structures are. On the other hand, if you're aiming to make it as readable and simple as possible for a non-programmer, I might recommend something that doesn't preserve all the perl details, like JSON.

Joe