Jeff Atwood extolls the virtues of Microsoft Log Parser. It provides a SQL syntax for querying log files of diverse heritages. It sounds very cool, and damn handy. From a quick look through the source he provides, I didn't see how to plug in new input parsers, though the architecture diagram he shows has a block for them. With CSV and XML inputs available, I guess you could transform anything you like into something it could eat even without plugins.