The only other "standard" fixed width font on the Mac is Monaco. There
are other fonts that claim to be fixed width, but I have seen several where
a punctuation mark (like a period to represent a stop codon, a dash to show
a gap or a colon to show alignment) breaks the "fixed width" rule.
DNAStar's products for the mac include a nice fixed width font that they
had designed specially for representing macromolecules. I recommend it.
Disclaimer: This is being posted to an UNmoderated newsgroup. However, I
will point out that I have no connection with DNAStar either as an
employee or a customer. Statements may include my personal opinions and
are shared for the benefit of others on the net. So there.