Teacher Discussion Forums

Hi; I am shopping for stand-alone English lang. instruction tapes my students can listen and learn with while they're driving their tractors all day long in the field. They are all Spanish speakers, a variety of levels. There are lots of taped language instruction courses out there, but I have no idea which are the best or most accessible to a variety of students. I think I need a range of material including language learning programs as well, perhaps, as some easy reader kind of fiction on tapes. I am NOT interested in the tapes that accompany books. Any recommendations for specific titles or authors would be appreciated.
Thanks,
Candy Meacham