My esteemed collegue Peter Orr pointed me to this free online site to learn and practice German: Deutsch-Lernen.com. The Lessons are very self directed and assume basic knowledge of grammar. For instance for Lesson 1 you are just given paradigms to learn with little to no instruction, but the exercises are helpful for reinforcing what you’ve learned. Another free website that Peter’s pointed me to is Babbel.com, and it has interactive, audio-visual exercises. Both focus on contemporary German, but if you can master how to use German then reading it makes more sense.
Another great resource for regular translation practice is the Theological German Blog. Also, let me remind you of Deutsche Welle, which a German website with daily international news reports written with non-native speakers in mind. It is read aloud slowly with a printed text, so it is really good for learning pronunciation.
Any other favourites out there?
[Update: Andy Rowell's TheologicalGerman.com, which was noted in the comments, is a good place to start as well. Thanks Ken for the comment!]
[Update2: Also, there is a decent online Theological German Grammar, by Walter Bense and updated Danny Zacharias]