The U-M Language Resource Center has subscriptions to several computer-based self-learning programs: Mango Languages, Foreigncy and Yabla. Mango and Yabla have German courses at several levels of difficulty. The LRC also has an extensive collection of language kits and videos. Some of the materials must be used in the Center itself, others can be checked out of the Center.
The Ann Arbor District Library maintains a sizeable collection of language learning materials, including materials for learning German. If you are a resident of Ann Arbor, you may obtain a library card at the AADL.