Exporting .WAV files from MuseScore
I've been using MuseScore's option of saving compositions as .WAV files, which come out sounding exactly like my original score. Since I use the Fluid sound font, the audio in .WAV format is far more pleasant than in most MIDIs -- certainly better than MIDIs played through Windows Media Player, which uses a wavetable synth, as I understand it.
After I've created the .WAV file, I then convert it to an .MP3 and trash the .WAV, since it's uncompressed and usually about 10 times larger than my .MP3. The tool I use for this is Pazera's Free Audio Extractor, which I originally downloaded for extracting the audio from video files, but you can find lots of other freeware audio converters in a Google search.
Caution: If you export a .WAV file, make sure you don't do anything else in MuseScore for a little while, because if the export process is still underway in the background and you use a menu or try to exit, MuseScore may stop responding. I found that out by accident, and since there's no progress indicator, I now watch my hard drive light until the activity seems to have stopped.