HexEd is a small hex editor with a turbo vision style interface. It is based on the spunk library and may be compiled for any system, that is supported by the library without source code changes.
There are probably hex editors with more features, but having the same user interface on many platforms is a nice thing too (there's even a native X version!).
Click here to read the HexEd doc file.
HexEd comes with full sources. For your convenience, source and binary RPMs for RedHat Linux are also available. Follow this link to download your copy!