I recently discovered after using a few different 'free' hex editors (Cygnus, Hex Workshop, Ultraedit-32 - you know, the free ones that are actually un-free) that the small number of files I had hex-edited had mysteriously and unexplicably reverted back to their original state, most demonstrably in the case of our custom Kobold .ska files, which were supposed to feature new custom kobold sounds but curiously did not in the CMF patches. Going back in and looking at them a second time showed that my changes did not 'take,' at least not permanently. (They did work initially though.) WTF that means I don't know, but I've since located a truly free free hex editor (freeware) that seems to work well. It is Hex Editor XVI32. http://www.chmaas.handshake.de/delphi/freeware/xvi32/xvi32.htm I further noticed after using this tool that there seemed to be far greater instances of the search strings I was looking for. Whether this is true or not or just an impression I had, I don't know, but if it is true that would be fucked up in a major way. After all, you're only as good as the tools you use, as they say. I would suggest that those of you who do hex editing check Hex Editor XVI32 out. If it proves to work well for others, maybe we'll replace the un-free Ultraedit-32 reference in the Downloads Forum with this one in the future.
Personally, I just use emacs (which is my normal text editor, but also has special modes for python, C++, binary files in hex mode, and all sorts of other bells and whistles). It is also completely free, in that it is both zero-cost and comes with all source code (in LISP). Check out http://ftp.gnu.org/pub/gnu/emacs/windows/ for a windows-native version. It has so damn many features that it takes some time to get used to, but by this point I've been using it for all my editing needs since 1992 and never had a complaint.
I've been using the same hex editor for years Gaear, nifty little tool that one, and you can't complain about free software. I did have a plugin for Beyond Compare 2 once, which allowed you to compare the contents of certain file types that the regular package couldn't, most notably .dll files, and anything else that needs to be hacked wide open with hex editors, though I can'tremember now whatit was called, or where I got it.