I think Chinese Learn Online is definitely one of the better programs out there. It is a gradual course which takes the learner from total beginner with no previous knowledge, and builds up from there. I used several of the podcasts for a Conversational Chinese course that I taught at our local junior college, and the response from the students was very positive. The methodology is very sound, and the real advantage is that students are not overwhelmed in the beginning, nor are they permanently stuck in a lower level.

I just love this course and tell everybody about it at the Chinese school where I have a 2 1/2 hour-lesson once a week. It complements and puts me several steps ahead of my presential classes - everybody feels awed by the sentences I'm able to build, my vocabulary and sometimes the explanations about a certain term that even the Chinese teacher is not able to explain (sometimes it's difficult for a native person to explain the mechanism of his own language, because it's just so intuitive and automatic for him).