Summary
german.about.com is packed full of information for beginner to intermediate German learners as well as teachers of those levels. In fact, there is so much content there that listing it here would take too much time! Instead, this article will highlight some of the things you can find on the site, and leave the rest for you to find on the site.
Of special note are the start learning section, practice materials, teacher resources, audio lab, grammar section, travel section, vocabulary section, culture section, thesaurus, games/exercises and verb conjugator.
There is a lot more there, and it's all accessible for free. :)
From german.about.com
Our German Language Lab offers audio for beginners or more advanced learners of German. Using the audio categories listed below, you can learn how to pronounce German correctly. By listening carefully to the sound in our German Language Lab, you'll have a model to imitate. Some language learners find it easier than others to get just the right sounds of German, but with a little effort you can do it! If you want to sound like a German, remember the German saying: Übung macht den Meister. (Practice makes perfect.)
Use the German Word of the Day (Wort des Tages) to expand your German vocabulary. Below you'll find two versions, one for beginners and another for intermediate or advanced learners.