There is a bdf font editor that comes with HP/Apollo workstations. It's called 'edfont'. It's not the best but it works.
Gary reports:
The standard X distribution for X11R5 contains ``xfed'', which allows you to play with BDF fonts. ``xfedor'' has a more elaborate user interface, and is available on most contrib directories.
The last time I tried:
``xfedor'' couldn't handle BDF files with more than 256 characters.
``xfed'' aborts if the BDF file contains a COMMENT line with no other text. The workaround is to edit the BDF file, to put text after the word COMMENT. A single blank space is sufficient. For some reason, the standard BDF files included in the X release contain blank spaces on the otherwise empty COMMENT lines. It was probably easier to add the space to the COMMENT lines of every BDF file than it was to fix the lex code for xfed. :-)
The GNU font utilities include an X-based editor called Xbfe which edits bitmapped fonts under X.
Eberhard Mattes' emTeX includes PKedit.