What... EMACS HEX Mode (I forgot what its really called) not good enough?
beav : http://linux.maruhn.com/sec/beav.html (big in BSDs, evidently)
hexcurse : webpage gone missing, but source is available lotsa places
hexer : http://www.mirkes.de...eware/tinyhex.php (un-maintained but useful)
ht : http://hte.sourceforge.net/
shed : http://shed.sourceforge.net
tweak : http://www.chiark.gr.../~sgtatham/tweak/