Just thought you might want to know that the two big Emacsen (FSFEmacs and XEmacs) come with hexl, which does exactly this. hexl is also used for hexl-mode, which allows one to edit files in this form.

Update in response to hsmyers's reply: You don't need to use Emacs itself to use hexl. It's a separate executable that takes ARGV and hexlifies it to STDOUT.