We don't see many Codonanthe or Nematanthus plants on the show tables (at least recently...), which is a shame because there are some very interesting and showy (and some big) plants in these genera. I'm also a fan of the intergeneric Codonatanthus hybrids that are available. Here's one, Codonatanthus 'Aurora', as entered in the National Capital Area Chapter's 2006 show:
The Delaware African Violet Society ran a three-part article in their newsletter - well worth reading. Here are direct links to the PDFs: November 2010, December 2010, and January 2011.