Lame comes with about every distro.
Creating an mp3 from wav the fast way:
...will ceate an mp3 version (file.wav.mp3)...
..but it will not give you real stereo and only a 128Kbits/sec bitrate.
For stereo and a higher bitrate(in this case you do need to type the resulting file):
lame -b 160 -m s file.wav file.mp3
(replace 160 with something like 256 if you wish so)
Also see "man lame".