I want to keep my learning experiance as much based on sound as possible, especially in the early stages. Podcasts of various types are a crucial aid and especially relevent to me as I get a lot of time where I can listen but not read or interact with a keyboard. Some Podcasts are learning podcasts and some are just material that can be used in a learning context.
I think that the Learning Learning Mandarin Podcast is a good example of a useful source of material.
The Learning Mandarin podcasts are not instructional as such. The usual format is that the host April discusses an issue, either something that has happened in her life of something newsworthy etc. Some of the earlier podcast feature interviews with Mandarin learners. Examples of topics discussed are two podcasts about traditional versus simplified characters and a podcast about the game (if it is a game) Second Life.
April speaks clearly and at resonable pace. Also the vocabularly seems to steer away from anything overly difficult or obscure. I can't understand much of it but some of the podcasts I could understand big chuncks of and I can often pick up the gist of the topic. If not there are plenty of easily recognisable words and phrases to work with.
The nicest touch is that you can purchase transcripts of the podcasts, the one I bought was just $1 (I could purchase via Paypal). This enabled me to download a PDF that contained both characters and Pinyin for the entire dialogue. I am not at my happiest when studying from text alone but alongside audio is great.