What can you do from here in California even before you go to the country?
Here are some of the materials I have found helpful in trying to keep up with my German:

A. Wikipedia, Google, and in German


B. Bibles and Devotional material
Read your Bible in German.
German Gospel Resources
Thru the Bible: German at OnePlace [available through iTunes]

C. Department store websites

GERMAN--Breuninger Department Store

GERMAN--Otto Department Store

D. News: sample websites

Kidon Media Link

GERMAN--News and Newspapers (MIT Libraries)

GERMAN--Google News

GERMAN--Die Welt

GERMAN--Der Spiegel


E. Television: sample websites


GERMAN--Deutsche Welle

F. LibriVox Audio Books in German

G. Books I have found useful:

Barron's German Vocabulary. ISBN 0-8120-4497-5
Easy Ways to Enlarge Your German Vocabulary
Teach Yourself German
Teach Yourself German Vocabulary. ISBN 0-8442-3985-2
Cassell's Colloquial German
Berlitz German Phrase Book and Dictionary. ISBN 0-8315-7845-0
Berlitz German Vocabulary Handbook. ISBN 2-8315-6392-5
Mastering German Vocabulary: A Thematic Approach. ISBN 0-8120-9108-6
Oxford 10,000 German Words. ISBN 0-19-283095-3
Oxford German Wordpack. ISBN 0-19-860336-3
501 German Verbs ISBN 0-7641-0284-2
2001 German and English Idioms. ISBN 0-8120-9009-8
The Complete Idiot's Guide to Learning German. 2nd ed. ISBN 0-02-863925-1
Harper Collins German Concise Dictionary, 3rd ed. ISBN 0-06-057577-8