Interesting websites (part1: some dictionaries)

The Internet is full of stuff which can help you learn English. It is sometimes extremely difficult to make good use of it, though.
That it why I decided to write here about some of my discoveries and favourite websites, techniques and tools I came across while surfing on the net.

Cambridge Advanced Learner's Dictionary (and more)
Although I would obviously recommend you to buy a printed copy of this dictionary, I am also aware that such books tend to be quite expensive.
Luckily the on-line version of CALD is available. It is somewhat limited, but nevertheless very useful and handy.
Although you can't actually listen to the pronunciation of the words, you can still read it using the international pronunciation symbols.
Each entry consists of a short definition, some grammar information and example sentences.
What is more, some of the words in the examples appear in bold font face. These are the parts of collocations (fixed combinations of words). So if you look up 'homework', you'll get 'do' bold, which means that you 'do your homework' not make. So if you are not sure which verbs combine with which nouns or prepositions you can always look it up in CALD. It is a great way to improve your English skills making it sound more natural.
CALD isn't the only Cambridge dictionary available on this website. Looking up a word, you can choose between Advanced Learner's, Phrasal Verbs, Idioms, American English, French / English and Learner's dictionary.

Other dictionaries and that kind of stuff
There are of course other dictionaries available on the Internet. It's probably best to look for them yourself, but still it's easier when you've got somewhere to start from.
Merriam-Webster (m-w.com) - American dictionary and Thesaurus (dictionary of synonyms). You can listen to the American pronunciation of the words here.
Urban Dictionary - a dictionary of English slang (mainly American, but not exclusively). The entries are constantly added, edited and rated by Internet users. If you want to understand some of the dialogues from American films or song lyrics, this site is a must-see.
Dr. Effingpot - this site isn't actually a dictionary place. However, it can still be considered useful in terms of getting to know British and American culture (through the English language). You will find there loads of British words and phrases (also slang) which can prove useless or difficult to understand in America and vice versa. Very amusing read.
Google - I will write about Google language tools some other time, but let me just drop a few words here on one, very useful and simple tool which can be used along with the search engine. Simply type 'define:word_you_are_looking_for' in the Google box and you will get a list of definitions found on the Internet. If you like, you can always follow the source link that goes with the definition and get forwarded to a specialised glossary of terms or a website devoted to the topic connected with the word you were looking up in the first place.