[mattdw]

HexFiend[1] doesn't do the trick? (I have only occasionally need for a hex editor, but it serves well when the need arises.)

[1] http://ridiculousfish.com/hexfiend/

[landr0id]

I believe I tried it once, but the UI wasn't very appealing to me. The key features I'm looking for are: fixed width of 16 bytes, clean interface, process inspecting (not sure how easy that is to do to be honest) and raw disk access.