There are hundreds of programs that do this. Lame is a good codec and easy to find/download. Programs used the underlying codec and do their thing with it.
Most more, the difference in the result matters not to most. Unless you plan to play the result on a $1000 stereo, you will likely not ever hear the difference if you use reasonable bit rates.
Picking the one that is easy to use and meets your $ goal are usually the initial considerations.
MP3 formats do make some difference, as higher bit rate files (128KB or higher) will tend to sound better than low ones (less than 96KB for example) on even PC speakers or iPods.