http://font.ubuntu.com

Ubuntu Mono has a free license and looks pretty good - we should include it as a font people could use along with the Bitstream one we've already got.

To do this, you'd want to include the actual font files in src/fonts and then double-check that they show up in the Preferences -> Main display tab.

FontManager.cpp should automatically pick up and load the fonts, so there shouldn't be any coding work necessary to do here.