I never tried paid ones.

I am right now using duolingo. Which is free.

Really great interface with explanation everywhere from every exercise, in case you make mistakes.

You practise, writing, listening, spelling, speaking,...And they have an App for Android/iPhone!

For beginner like me it's great, don't know for advanced ones.

Otherwise busuu is free also but I really prefer duolingo now.

the only thing that worries me a bit with ling q is that there doesn't seem to be very much at all for grammar, and that is the the bigest weakness i have in my german at the moment that i was looking to strenghen! how do you rate duolingo for grammar instruction? 

Well... I'm at the really really beginning of the courses so don't think that I have a full and objective point of view but for the moment, each time that I make a grammar mistake, they give a clear explanation so that I won't do the same mistake again. They don't just tell you WRONG and click next, they tell you why. Even the accent or capital letter for name.

As it's fully free, I would recommand that you give it a try for 10min and see if the grammar instruction is enough for you ;)

yup will do. thanks for the suggestion! 

My husband and I both used Rosetta Stone. We started in August. He likes it more than I do. I really like knowing the rules of the sentence structures and the do's and dont's. While my husband really likes that it is more intuitive and everything being in german. I really believe it depends on your style of learning and finding the right program for your style. Best of luck!

Check out Duolingo.  I am actually doing a combination of Duolingo and Rosetta Stone, but I think I actually like Duolingo better as it makes me translate from English more, which I find more challenging.  In addition to the website, they have a pretty slick app as well.

cheers for all the suggestions. i've started using duolingo and there's some bits i like, others not so much. I've also discovered that putting your phone on silent doesn't mean that the app will not speak loudly on the train to announce that "Der Mann isst Nudeln" over and over to all the other passengers until i plugged in my headphones :) 

will also give Rosetta Stone a try then as the grammar side on duolingo isn't quite up there for me. 

you can try lingq.com

Buusu is a good language site (Swiss)

I started with deutsch interaktiv on the site deutsche welle.

http://www.dw.de/learn-german/deutsch-interaktiv/s-9572

They have a lot of material besides this one. There's some exercises about grammar with immediate correction. It goes until level B1. But I would suggest really grammar books if that's what you're looking for. This computer programs are more about vocabulary and repetition. Like a method of immersion on the language. It did not work so much for me. Too old, I do not learn intuitively anymore.

I suggest these books:

intermediate - http://www.amazon.de/%C3%9Cbungsgrammatik-Deutsch-als-Fremdsprache-Mittelstufe/dp/3190016577/ref=sr_1_20?ie=UTF8&qid=1390255489&sr=8-20&keywords=deutsch+grammatik

advanced (I'm using this one in my course) - http://www.amazon.de/C-Grammatik-%C3%9Cbungsgrammatik-Deutsch-Fremdsprache-Sprachniveau/dp/3941323113/ref=sr_1_56?ie=UTF8&qid=1390255560&sr=8-56&keywords=deutsch+grammatik