I know I've written about MIDI in Linux before, but I thought I'd share another alternative to people who prefer using SoundFonts - fluidsynth. The advantage is that there are several high quality soundfonts available for download all over the web and you can use the qsynth GUI tool to easily to control the MIDI output.

For users of Debian or Debian-based systems, setting up fluidsynth and qysnth is as easy as using the apt-get install command. Additionally you must download at least one SoundFont to use with it. Just search the web for some free SoundFonts (you might want to download a GM-compatible one for portability). Like all software synth, fluidsynth is also fairly resource hungry and will eat up plenty of CPU cycles. However, it's a good option for those who don't have hardware MIDI and still want to use SoundFonts.