TrID is a utility designed to identify file types from their binary signatures. While there are similar utilities with hard coded rules, this has no such rules. Instead, it is extensible and can be trained to recognize new formats in a fast and automatic way. It uses an XML-based database of definitions which describe recurring patterns for supported file types. You can help creating new definitions. Just run the TrIDScan module against a number of files of a given type. The program will do the rest.
http://www.ziddu.com/downloadlink/4317347/trid_w32.zip