Vorbis GT3 is a quality improved version of the Vorbis 1.0 encoder. It is currently unfinished, although beta versions are already available.
It is a drop-in replacement for standard oggenc, supporting the same options. Tuning was done for quality levels 5 to 10.
Current version is beta 1.
Another tuned Vorbis encoder that may deliver better quality is aoTuV.