Rosetta Stone auf Deutsch
I purchased the 3 levels of Rosetta Stone in German after completing introductory college German. The program offered an incredible method of learning pronunciation, spelling, and just how to identify what sounds right. "Er springt von dem Boot" sounds better (because it is correct) than "Er springen auf das Boot" even though the latter would seem like a better English-German literal translation. Formal classes are usually very grammar-intensive and often fail to provide legitimate speaking and communication skills.
However, I do feel that the grammar theory from class helped me to better understand what I was seeing in Rosetta Stone. If I were to recommend a course of action for someone serious about learning a language, I would say: Take an introductory course in high school, college, or a trade school to get a grasp on grammatical principles, the theory behind sentence structure, and cases, etc. Then invest in all three levels from Rosetta Stone and work through them doing no less than about an hour a day until finished. Then get on an online book/movie store and buy a few discount movies and books in the language or rent movies. These will allow you to build vocabulary through context (and if you get really stumped, use of a dictionary is not a crime).
The best way to learn a language always is by immersion into it with no translation from your first language. Though Rosetta Stone cannot each you everything, it is still an exceptionally effective method of foundation building.