Synalyze It! is a groundbreaking app which lets you easily edit and analyze binary files of any size. Synalyze It! features enhanced support for many character encodings and it will allow you to interactively define grammars for various file formats.
Here are some key features of Synalyze It!:

Hex Editor & Viewer
Definition of a "grammar" for binary files with Scripting support
Export grammars to GraphViz (only in this Pro version)
Automatic installation of existing grammars
Export of analysis to XML or text (only in this Pro version)
Data view for common variable types (only in this Pro version)
Multi selection of results (only in this Pro version)
Go to position item in toolbar (only in this Pro version)
Lua scripting element (only in this Pro version)
Edit description of structures and elements (only in this Pro version)
Change Font in hex view (only in this Pro version)
Printing
Histogram view
Checksum / hash value panel (only in this Pro version)
Go to Position in file using expressions
Save selected bytes
Compare code pages
Incremental text search with encoding selection
Find text
Find numbers
Search for masks
See all strings in a file