I've not used it much myself; largely because I came across a different language learning thing online that's very, very different, but unfortunately doesn't do many languages, and only one of them is particularly popular among language learners. I used it to learn Welsh, and I've found it really, really useful. It's called
SaySomethingIn, and it is audio only. You get an English prompt, and you give a response in the language you're learning, then you hear the correct answer from native speakers (the pause button is useful here - the lessons are all mp3 files). You spent about half an hour per lesson doing this, with the occasional pause in the middle where you're given a new pattern or piece of vocabulary. You don't learn a wide vocabulary using these lessons, but you learn enough that you can spend a week only using that one language (with a little bit of miming, talking around a subject or simply pointing at an object and asking what it's called), and what you lose in terms of having a wide vocabulary (which you can always pick up elsewhere - I hear there's this pretty decent site on the web, but I forget it's name
) you gain in being able to relatively easily use what you do know. I've heard the course described as Michel Thomas on steroids, so if you've heard of those courses, then make of that what you will.
Currently they do Welsh, Spanish, Manx, a little bit of Dutch, a little bit of Cornish and two lessons of Latin, with the most developed courses being the first two, though they have recently developed a tool to speed up the process of creating a course (the Manx course is the first course to use it, and as a result it does have a few minor issues to sort out). The intention is to also use that tool to make courses in other languages (in part because it'll mean that Wales might see tourists who do speak Welsh but don't speak English, making the language more useful for businesses, and in part because it just opens the business up to a wider consumer base). They did have an English course and a Welsh course through the medium of Spanish and a Spanish course through the medium of Welsh, but those have been taken down until they can be replaced by something better.
Prices vary based on language, but are fairly low and are in Stirling by default so for most of you will be even lower than usual
. Welsh is the cheapest, at £5 a month with the beginners' course being available for free, simply because the makers of the course are Welsh and they want to make it cheap and easy for people to learn the language, while Spanish is a bit more expensive (I believe it is priced per five lessons instead of having a subscription, with the first 5-10 lessons being free) because they actually want to make a profit. Not sure about the others.
Edit: Oh, and they use dialog based listening practice sessions which play at double speed, with the intention being that after a while, you'll get used to the double speed and will have an easier time understanding people who speak quickly naturally. They're also ambitious (read: nuts) enough that they're aiming to provide sufficient material in each language to give the 4,000 most commonly used words. I have no idea whether that has any shot of actually working, but it'll be interesting to find out...