See also the TLG technical document on the proposal to encode Greek metical characters in Unicode, which can be found at http://repositories.cdlib.org/tlg/unicode/15/
Brill have released some advice on symbols for metrical display (http://www.brill.nl/downloads/Metrical-Characters-Unicode-updated.pdf)
This issue was discussed at some length on the Unicode Ancient Languages list (see e.g. http://lsv.uky.edu/scripts/wa.exe?A2=ind0110&L=unicode&D=1&O=D&P=235 or go to http://lsv.uky.edu/archives/unicode.html and search for "metrical" vel sim.).
The only fonts we have found to do so reliably (as per November 2006) are:
Others suggestions of suitable fonts are most welcome.
More advice on this topic may be found in the archives of the Unicode discussion list.