I just found this podcast as I randomly looked for Mandarin study online. It's really superb once you get to the level where you can understand most of it. Listening practice, even if you don't understand everything, is crucial. This is my 5th foreign language. She has transcripts of the podcasts on her site, so I'll probably buy the set. The textbooks look pretty good, too, as I'm working on expanding my character knowledge.

I really like April's podcasts. I am learning Mandarin. I find her speaking style very pleasant. She speaks clearly, properly, and not too fast. Very helpful for real world listening practise.