I still use smart.fm as my primary app for language education. But since the goal here is to master Chinese, not shrill for a single program, I had to look elsewhere. Thanks to Hacker News, I found nciku.
nciku deals with exclusively Chinese-English (and vice versa) education. So many of the features deal with organizing all the Chinese characters.
My favorite has to be the character recognition feature. It allows me to write a character with a mouse (or in my case, a wacom tablet) and it will try to match the word. Great if I’m trying to read print articles (it’s also a browser toolbar)
Another important feature is the ability to create conversations. What is good with knowing all the characters if one cannot string together a sentence. There’s a big collection of conversations, or you can create your own.
I haven’t used all of the features yet but I definitely recommend this site for Chinese-English education.