James Duncan Davidson recently wrote [an article about monospaced fonts on Mac OS X](http://duncandavidson.com/archives/654).
He mentioned Bitstream Vera Sans Mono as a great replacement for Monaco — the standard monospaced font packaged with OS X. The blog readers quickly added more fonts: [Inconsolata](http://www.levien.com/type/myfonts/inconsolata.html) (my favourite now), DejaVu, Panic Sans, [Envy Code R](http://damieng.com/blog/2007/08/19/envy-code-r-preview-6-released-with-visual-studio-italics) and more.