Soundclash Radio (www.soundclash.org) happens every wednesday on real airwaves (also listenable live online) but they archive every show on the website, and they're just ace. Great selectors, rare tracks you thought you'd never hear, and important guests (interviews and selectors. They throw in nice Soul, Hip Hop (no mindless rubbish though), Jazz and Funk in the mix but it's mostly JA music.
There are some good podcasts that explore all styles of JA:
http://www.podlounge.com.au/listfeed.php?feed=29763 Double Barrel Sound System
http://mobtownskasounds.podomatic.com/ Mobtwon Ska Sounds