HexEdit is a hexadecimal file editor for the Macintosh. The most widely used editor of its kind on the platform, HexEdit can handle file sizes of up to four gigabytes with ease, yet has memory requirements of less than a megabyte (with colour turned off).
It can also compare files for similarities or differences. At the moment there are 680x0, PowerPC PEF and PowerPC Mach-O builds, but an x86 build will be coming soon.
Works well for me on Lion 10.7.3. And I like the 'Hex' icon! Good to see the Dev has a sense of humor!