I may have mentioned that I'm studying Spanish, and that I have a demonstrated anti-talent for languages. For what it's worth, here are some of my experiences to date.
I started off with Rosetta Stone Latin American Spanish. It's expensive, so I only bought levels I and II. Probably un error, since when I later bought all five it was cheaper to buy I-V than III-V, or nearly so. Rosetta Stone calls their method dynamic immersion, and essentially all instruction is in Spanish. The idea is to learn as a child does, by a combination of context and point and say. For example, they will show a picture of an apple and display una manzana, while a native speaker is heard pronouncing it. You are confronted with a series of choices to pick, speak, or write, and correct answers get a more or less pleasing sound while wrong ones get an less pleasant one.
You need to learn pronunciation by imitation, a task that was difficult for me. There are some sonograms which I found very unhelpful. The lack of formal instruction in sound or grammar was a significant handicap for me, one that became more onerous as more tenses and other grammatical elaborations were introduced.
The strongest aspect of the lessons is the structure of the content - you learn the vocabulary and grammar most essential to the prospective traveller first. Another exceptionally useful aspect is continuous review. The computer keeps track of your progress and how long you have been away and schedules you appropriately. I have so far completed Level II, and made a resolution to finish III this year.
Why so unambitious? Well I decided that I really needed to go back and study some formal grammar and work on my vocabulary before I continued. I have now acquired several books on Spanish, a couple of which look really good. More on them later.
Needless to say comments, suggestions, and your own experiences are welcome.