I've been re-reading an old copy of Barry Farber's book How to Learn Any Language. The copy I have is more than a little out-of-date, as the author talks about the "innovation" of portable audio-cassette players as a language-learning tool. The internet has opened up countless new tools for learners of foreign languages. If I were to update Farber's book myself, here are the online tools I would add to his list of advice. If you would like the details of any language-specific sites or need help navigating the overwhelming amount of available online resources, feel free to contact me through WyzAnt by email to set up a tutoring session. (I specialize in tutoring Chinese, Japanese, Spanish, and English, but I have also "dabbled" in other languages).
Online dictionaries that provide two-way look-up are usually much easier than looking up words in a paper dictionary, especially for character-based languages like Chinese and Japanese.
Podcasts online are plentiful in many languages. Whether you are looking for lessons in English to teach you a foreign language, or for a total immersion experience in your target language, you should not have much trouble hunting down hours of (often free) audio online.
Streaming internet radio is a good choice for an advanced learner looking to improve vocabulary or even for beginners who want to be immersed in the sounds of the language. Listening to the language in the background on headphones while going about your day can really help improve your pronunciation.
Movies in your target language can be viewed online, as well as a plethora of music that can be downloaded. Searching for the lyrics to songs in your target language with an English translation can be another great way to learn vocabulary.
Language-learning websites connect native speakers and learners of all levels for chatting in your target language, and some sites even allow you to submit written posts for native speakers to correct. English is one of the most popular languages for people to learn, so correcting other learners' English posts is a great way to make friends that will return the favor by correcting your posts in the language of your choice. Some people will even want to take your online "friendship" a step further and communicate by Skype. As with any online relationship, make sure to exercise caution in this area.
Finally, websites about languages usually provide explanations of grammar, as well as some basic words and phrases. Bookmark your favorites, and return to them frequently until you "graduate" to the next level. Then move on to a more difficult site. For the advanced learner, try reading the foreign version of familiar websites with the help of easily downloaded tools that allow you to hover over a word on a website to see a pop-up of the definition and pronunciation of the word. Change your homepage to the language you want to learn! If your computer is your own, change your interface language! Above all, have fun!