Code formatting messed up...

[ijabbott]

If you like the look of the old Courier font (or want it for Postscript compatibility), the TeX Gyre Cursor font is a good substitute for Nimbus Mono L, as it has the same metrics and greater coverage, including the most common Greek characters (including the ones used as technical symbols).

On Debian (and probably Ubuntu and Mint?), the fonts-texgyre package installs the OpenType format of the TeX Gyre font family, and the tex-gyre package installs the Type 1 format of the TeX Gyre font family. As you can probably guess from the name, they are intended to support the TeX typesetting system, but are also suitable for general use.

Another option is to use the Courier New font as used by Microsoft Windows, but that has different metrics. On Debian, it is installed by the ttf-mscorefonts-installer package.