I recently made a serious attempt to learn Chinese, quite intensively, and ChinesePod.com was the main method I settled on. They release a 10 minute podcast each day: there are various levels but you can expect least one new newbie lesson each week, and there are over 160 archived lessons you can access.
The site is subscription-based, though the podcasts themselves are free (in fact, they are under an open source license). The first level of subscription gives you a PDF transcript. Not too expensive ($5 to $9/month), but, still, I think there is little value in it.
The premium subscription is more expensive ($20-$30/month) but much better value. It adds expansion sentences (each with audio, hanzi, and pinyin/English on mouseover - wonderfully helpful), and exercises (very nicely done, in Flash: drags words into the blanks, match up Chinese and English, choose correct Chinese translation of an English word, etc.).
There is higher level of subscription, which is an 8-week course ($400) with daily phone calls with an instructor. I have not tried it.
Every lesson has its own discussion board (open to non-members as well) and the staff are very good at answering questions. In fact you can find some real gems of explanation and vocabulary on the discussion boards.
The downside of the premium subscription is that it is only good value if you are studying intensively: in other words if you will be able to do a lesson each day. Conversely, that can be good, as it inspires you to study intensively: trying to squeeze as much into the month certainly helped me.
There is a 7-day free course, during which you can try out all content on the site. As mentioned above: save it for a 7-day period when you will be able to give it some focus.
Overall, highly recommended for anyone serious about learning Chinese:
I have a few specific criticisms, which is really just feedback for ChinesePod.com, but I thought it makes sense to put it here too.
* In every example sentence with a surname the person is either Wang or Li. This is missing an opportunity to introduce other surnames. (Surely not everyone in China is called Wang or Li??)
* No guidance on which lessons to do. After doing the 7-day free course I chose the newbie business lesson subset, which I imagine is very common, but it immediately uses words that have not been introduced.
* Old lessons are not as good as recent lessons. It seems they have experimented with the style over the 160 newbie lessons, and made many improvements. (The lesson level is more consistent - easy - in the newer lessons).
But the old lessons are still up there. I personally think their effort would be better directed in re-making the early lessons than in putting up a new lesson each day. Which is probably unacceptable to the marketing department. So in that case I think early lessons should be removed if they are not up to standard.
* Flash cards. Each word has three forms: hanzi, pinyin, English. Flash cards really need to show the other two when you turn it over; currently they are not useful. I believe this will be addressed at end-March.
* The pop-up showing pinyin and English is wonderful. But it misses some words, which is very frustrating. Again, I have heard they are working on it.
* There is no listening comprehension in the exercises. I.e. listen to a sentence and choose the word you think you heard. A surprising omission as they already have both the content and the technical skills.