In June, 1999 the Radium group released their improved FhG codec.
If you want to encode mp3 files at bitrates of 128kbps or below, it has been proven that a FhG codec yields superior fidelity. Mind you, this is at the expense of encoding time. You can balance this a bit more by refraining from selecting the High Quality option, should it be available. Those of us with processors 466mhz or slower may not be able to encode in real time. In this case, LAME makes a suitable alternative.
As for codecs, there are two varieties of them; both internal and external codecs. You can use the latter in any program with codec support, while the former is licensed for use in one specific program. The Radium FhG Codec is essentially an internal release made external with some assembly level optimizations for a 5% - 12% speed increase on Pentium CPUs, courtesy of igNorAMUS.
If you're wondering where you can find it, that shouldn't be too difficult. Any popular search engine should be able to fulfill the task. Once you've decompressed and installed it, I recommend leaving the configuration as it is. You might take a look at the included FAQ for additional information. It should appear in your codec listbox as "Fraunhofer IIS Mpeg Layer-3 Codec (professional)."
Happy encoding, and don't forget to share.