I'm typesetting quite a bit of sheet music with lilypond these days, and it helps a lot with proofreading to check the midi output with timidity. Plain vanilla timidity will play piano only, which can be quite cumbersome for more polyphonic pieces.
Luckily, there are sound patches for all those who always wanted to hear the Ninth performed by the Silicon Valley Midi Philharmonics.
Download freepats, move and unpack it.
> sudo tar -xjf freepats-20060219.tar.bz2 -C /usr/share/timidity
This should give you a 'freepats' directory from the archive. Make the directory readable for everybody.
> sudo chmod -R a+r /usr/share/timidity/freepats
Edit the config files:
> sudo vi /etc/timidity.cfg
Add these two lines somewhere in the file:
Try it on some midi file.
Some timidity usage tips: the -ia, -ik, -ig, -im options give you a GUI where you can scroll through the file etc. timidity -Ow foo.mid generates a .wav file.
(adapted from linuxwiki)