Although there is supposed to be a monospace font in the family, the default package doesn't come with it. I tried getting ttf-ubuntu-monospace but there aren't any packages with that name. How/where can I get the monospace font?
Ubuntu Monospace comes preinstalled with Ubuntu 11.10 and it is the default terminal font.
If you want to install it on non-Ubuntu or pre-11.10 machines, download it from font.ubuntu.com!
The Ubuntu monospace fonts have been released since this question was asked: http://font.ubuntu.com/
or you can use google fonts
and get it easily by downloading
the font, getting the link, or copy the necessary code.