Skype, unfortunately, is still far and away the best affordable solution, particularly for audio. Few tips to improve Skype for podcasts:
-Disable automatic microphone controls in sound preferences for everyone involved. Skype will automatically adjust levels of audio, which generally leads to bad results. You want to be able to have that control.
-Always, I mean always, make sure your guests are wearing headphones/ear buds and that they know general microphone technique(talking past, not directly into the mic for starters)