Heme’s a simple hex editor for Linux. It actually compiles and works on Mac OS X too but some of the key mappings aren’t quite right. It’s on sourceforge at http://sourceforge.net/projects/heme/
I actually made a small contribution to it’s codebase too. Including at least one bug! I also fixed said bug when I spotted it 😉
The advantage of it is that it’s so simple it’s really likely to compile. It’s functionality is a bit limited but I could always expand it some more. A lot of the other hex editors I found wouldn’t compile or had dependencies I didn’t like.