Hexedit

Hexedit is an editor which allows editing and viewing of a file or disk in hexadecimal, along with it's ASCII or EBCDIC text equivalent. Standard editing features include insert, delete, search (text or byte searches), highlighted changes, undo, two different viewing formats, base converter, and full screen text snapshots. Editing fixed disks (i.e. /dev/hda) in Linux and OpenBSD is supported. Color terminals are supported.