There are many network analysis tools like Wireshark, Sniffer Pro, Omnipeak which can dump the packet data in structured manner. I'm just writing my own file analyzer for general purpose, which can dump JPEG, PNG, EXE, ELF, ASN.1 DER encoded files, etc. in tree style. There are so many file formats in the world that I can't handle them all. So I'm wondering if there's some software already there, with pluggable architecture and a large established file format repository?
Bonus: If it's for Linux and free.

filetells you the type of a file, andstringsprints strings in a (possibly binary) file. Although both are a far cry from what you're asking, they're nonetheless good to know about. – Joey Adams Dec 27 '10 at 6:36