1. My primary advice would be for you to check out the list of links on our course website.  It contains links to everything under the sun, and if you play with these links a little every day, you can learn a lot and have fun while you're doing it.  In particular, you'll find links to:

Miscellaneous websites where you can watch German TV programs or listen to German radio "live" or "on demand" over the internet, which is a great way to see and hear authentic German

Band homepages and websites with music lyrics

Online newspapers and magazines

Miscellaneous humor sites, including the complete text of The Life of Brian auf deutsch

Movie homepages, movie reviews, movie schedules

Full texts of lots of literary, philosophical and religious texts (including the Bible)

Recipes; Menus from German restaurants and university cafeterias

Online art galleries

Fashion

Sports news

Scientific and popular scientific news and articles

Online dictionaries and German courses/exercises

Homepages of some German or German-American companies

Reference works in German

Computer-related sites

2. For more structured practice, you can refer to some other features of the general German course website, such as:

• a list of the most frequent German words (learn these 200 words, and you'll know 1/3 - 1/2 of the words in just about any German text!).  Lots of these words will already be familiar to you, but spending some time making flashcards of the ones you don't know and then periodically reviewing those would be a very worthwhile investment of your time.
• the Interactive Grammar Tutor.  Especially useful:
• the "Basic Chart" of der- and ein-word endings and of the forms of the personal pronouns (also lists the cases associated with the most common prepositions)
• the two "Case Overviews" summarizing the German case system; the second one especially may help clarify when to apply which of the various rules you have learned about case
• the summary of Verb Tenses

3. Watch German TV. Soap operas and kids' shows are especially good for language learning. Unfortunately, the International Channel and GermanTV are now defunct, so to watch German TV, you'll probably have to follow some of the links already mentioned above to sites where you can watch German TV on the internet.  

• If you have access to the Language Resource Center or to any of the rooms with built-in TVs in the MLB, or if you are living in a dorm room with UMTV, you can watch Deutsche Welle TV on UMTV channels 12 and/or 76. Deutsche Welle TV broadcasts news programs and interesting documentaries on a wide range of topics, including music, science, current affairs and economics.

4. Watch German movies!  Even the big video stores have pretty good foreign film sections these days, and you could ask the clerks for help in identifying which movies are German with subtitles (as opposed to dubbed).  In Ann Arbor, Liberty Video is especially good: they have a whole rack full of German movies.  The list of German movies on reserve at the Language Resource Center (including links to info on these movies in the Internet Movie Database) is always available on the course website.

5. The language courses they sell at stores can be a helpful supplement, if you want to spend the money for them. I mean the ones with CD-ROMs and/or CDs/tapes.  You would hear lots of German, and get a fairly systematic review of fundamentals plus lots of emphasis on conversational skills.  I haven't tried any of these (==> please take this advice with a huge mouthfful of salt), but...

• Our Language Resource Center has gotten lots of enthusiastic feedback on the Tell Me More series of CD-ROMs, so on that basis, this is the software I would recommend most highly. For this and any other such materials, you could check the reviews at amazon.com for more info (bearing in mind that just about any product, no matter how inferior, will have some rave reviews at amazon.com, and also, that just about any product, no matter how excellent it is, will be trashed by some people there)
• Based on my high opinion of some of their dictionaries and other materials, I would think that a language course by the German publisher PONS (possibly marketed by Harper Collins in the US) could be very good, if you're able to find one.
• I'm skeptical of the Rosetta Stone method, but know that some people swear by it ==> would definitely recommend trying it out carefully before purchasing it. The picture-based method they use is very effective for teaching vocabulary (though I'm not sure how long you would retain what you learned without using the vocabulary more actively than what the program gets you to do), but you would want to look into how well the software is able to teach you grammar, reading, listening, pronunciation, etc.
• I've heard some very enthusiastic comments about the Pimsleur method, but have also heard it described as excruciatingly slow.
• Some cheap audio-only introductions to various languages that I think are quite ingenious for getting people a "running start" with a language are marketed under the title Learn _______ with Michel Thomas. His method is to introduce a few simple cognate words, get students to form some sentences with them, and then alternate introducing more vocabulary and some simple grammar with new tasks for students, so that one is always actively processing the new information. One ends up with a somewhat odd selection of vocabulary, he speaks German with an accent, and he may make a few mistakes, but nevertheless I think that for a relatively small investment of time and money one learns quite a bit, and is then better prepared for using a more systematic and comprehensive self-study course.
• I would guess (but don't know) that anything with the Defence Language Institute's approval can't be too bad. 
• I would stay away from any "Hugo" course, based on a very poor German text of theirs I saw some years ago - but my bias against them may be outdated.

6. A good library, or most Borders stores or similar places would carry some German newspapers (probably the dull ones) but also some magazines that might be fun.  Check out the list of links I mentioned above for online newspapers.  In particular, for German tabloids, a good link might be http://www.bild.de.  This is the Bild Zeitung, a repulsive newspaper I've vowed never to read again, but its German is simple and great for learning, and the sensationalism helps keep one's interest for a while.

7. For some ideas on how to find German music, and some artist names and song titles to look for, check out this German 221/231 activity on German music. Bear in mind that this was written by someone over 40, and that e.g. a German email pal [see below] would be able to give you a much better idea of what's hip right now

8. Anytime, anywhere you can think in German about what you're doing and seeing as you're doing and seeing it.  This will help you in particular to get to know the words and constructions that are most relevant to you personally.

9. You could find a German email pal. Click here for an annotated list of sites that will help you find German email pals for free.

10. You could buy a dual-language book, or try reading a German translation of a book you like and know.  This is a great way to learn if you have the discipline not to overuse the translation.  If you're in Ann Arbor, try checking a book out of the free reading library in the LRC.  Incidentally, you can turn many websites into a "dual-language book": if the site is available in German and English, you can open a second browser window and read the two versions side by side.  Or go to the Grimm fairy tales site, where you can click on the option of reading the texts with a facing translation.  For an annotated list of some other recommended books, generally available in the bookstores in Ann Arbor, but otherwise easy to get via www.amazon.de, click here.

11. Find some American friends who are into speaking German. Or some old German Americans.  Or some German tourists....