From the MPegger web site:

MPegger was a pioneer in MP3 encoding on the Macintosh and remains a powerful digital audio tool. It supports both MPEG Layer II and Layer III (MP2 & MP3). Normalization and direct encoding from SoundDesign II files make it an easy choice for high-end digital musicians. CDDB access makes labeling and archiving your music collection a snap. And MPegger is fast, with support for variable bitrate (VBR).

Version 1.1.1 update fixes a crash which can occur when encoding to MP2.