Chinese Pod The best. Nothing else really comes close. It's affordable, too. Last we checked, ten dollars a month gave you access to all of their learning materials, which can be downloaded. The entry level lessons are concise and much more engaging than your typical textbook fare, and an affable Irishman and his Chinese assistant make the learning process lighthearted and fun.

Chinese Learn Online Sort of a poor man's Chinese Pod, this series is hosted by what seems to be the most boring man in Canada. Less hip and less topical than Chinese Pod, it never-the-less has the advantage of being more like a textbook, with a linear progression from lesson to lesson. Also, the direct translations offered by the droning host of the show are really quite informative, and especially help if you are learning to write the characters as well.

Zhongwen Red An interesting free site that promises to have a lot of content. Currently, it's still under construction, so we will have to wait and see.

NCIKU Madarin Dictionary Our favorite online dictionary of Madarin, this site features example sentences, collocations, and idioms in addition to the translations. Perfect for students!

Chinese-Forums One of the best forums devoted to learning Mandarin out there.

Chinese-Tools A great site with a series of basic lessons that build on each other. Based on a Chinese textbook. The really good thing about this site is all the mp3s available for download.

Zhongwen Blue This is a sister site to Zhongwen Red, which likewise is an absolutely free resource for learning Mandarin Chinese. Very good for what it is.

CChello They have a series of free podcasts based on the notion that even the mentally retarded and chronically lazy can somehow learn Chinese if it is condesed into as short a time period as possible. Like a shot of tequila or a kick in the groin, it's a good way to jumpstart a study session, because the five minute lessons really are jam-packed full of useful stuff. Unfortunately, the ipod lessons and the pdf files don't seem to be synched, which makes it dificult to study away from the computer.

Instant Speak Chinese A great site but a bit expensive. You get 100 lessons with a six to ten line dialogue with each lesson, as well as vocabulary and some expansion exercises. Some parts are suspiciously similar to Pimsleur's Chinese course.
Zhongwen Green The last in the Zhongwen series, we feel that the layout for this site is the best, although the vocabulary is a bit redundent. Still, the extra listening practice is nice.

World Learner Chinese A very sanitized and basic "series" of lessons that you can listen to online. It's a nice second look at some key vocabulary, but come on, do you really need two lessons devoted to "Tomb Sweeping Day"? It's completely free, though.

Chinese for Travel Exactly what it says it is. Not good enough for a stand-alone course, not by a long shot. However, it is absolutely free.

Xue Hanyu Online A lovely site that shows great promise. Well thought-out lessons move fluidly from one to the next.

Primezero Chinese Tools has a good free Hanzi to Pinyin converter, as well as a dictionary that includes common colocations of the major characters.

Zap Chinese Am online phrasebook of some use.