For students who can read English, but who struggle to understand native speakers, the “Learn English by Radio” series of iPhone apps is very helpful and four of the apps are now free! It has variable speed audio, which is super useful, and synched transcripts with lots of links to idiom, vocab, grammar, and pronunciation clarifications. And it’s fun- it is based on classic American radio shows like Dragnet and Gunsmoke. Here is a link to one of the apps:
https://itunes.apple.com/US/app/id571324367