Good log analysis tool for nginx?

[Rt Ibmer]

Can anyone recommend a good log analysis tool that is a good match for nginx? I'd like something that is flexible, where I can tell it which fields in the format are for which parts of the data (i.e. user agent is field 6) etc.  Thanks!  Note that I am looking for a SERVER SIDE tool to process the nginx logs (JavaScript based analytics tools will not work for this particular application).