Matt guested on LifeHacker recently, and produced a handful of nice articles. How To Enjoy Audiobooks includes some good suggestions, and links to two threads on Ask MetaFilter about finding good books and good readers.

Andre adds mentions of Project Gutenberg audio books (read by human volunteers, and computers), which in turn mentions AudioBooksForFree.com and Literal Systems. While not necessarily sources of high quality readings, the fact that they're free means you can easily go sniffing for gems.