|They teach languages very well.|
For online resources, one company has created Livemocha, an interesting attempt to combine social networks and language learning. It's free (though there are many advanced services you can pay for) and you work through a series of lessons in your target language. They help you with spelling, grammar and pronunciation and then you ask friends or strangers to correct your work. My wife isn't keen on the site as she claims that (for French) many "native" speakers were giving incorrect advice. You can rate the advice you receive, but since you presumably don't know the language you're studying, it's hard to know if the advice is sound. Also, all languages start out with the same standard set of words and while they may teach you the language, the starting vocabulary ("I am a boy!") isn't helpful in day-to-day situations. Still, it's a free and it's fun and I hope they continue.
For discussions about learning languages, you should check out How-To-Learn-Any-Language.com. This is basically a huge message board for those who love to learn languages. They're pretty down on traditional classroom learning (something which I think can work better than they claim), but they have speakers of a huge variety of languages and, more importantly, they can point out some of the more useless language learning material out there. Check out their FAQ for a great overview of the site and about language learning in general. Sadly, some of the more important links on that FAQ are broken, but you can sign up on that site for free and search for what you need.
If you want to spend money on learning a language, I have some recommendations. First, you probably never heard of it, but you must check out Assimil. Originally developed in France to teach English to French people, it turns out to be an incredibly well-regarded method of teaching languages, even if you're studying on your own. It has a "passive" phase followed by an "active" phase after a couple of months. It consists of daily half-hour self-study lessons and it's fun. Also, perhaps because they don't have to pay the huge marketing budget which some companies do, they're a fantastic value for the money.
Of course, the well-known Pimsleur method has to be mentioned here. It focuses almost entirely on spoken language, so you'll have trouble reading and writing. You'll also only develop a small vocabulary of perhaps 500 words at the end. However, that vocabulary should be perfect. Your pronunciation should be excellent and you should also have a good handle on the grammar. Few courses get pronunciation right the way Pimsleur does. I often see it recommended as a great supplement to your primary course.
Be careful and do your research about language learning courses. Many of them have great reviews around the 'net because either people don't know better or, in at least one case I've heard of (but don't want to get sued over), they have a lot of web "affiliates" who say nice things about them. Money appears to change hands. As a general rule, the more marketing is involved, the more suspect I think you should be.