Dictionaries

My favourite online dictionary is probably the Oxford learners dictionary. 
I consider it very trustful source and very helpful in my studies. You find there everything you need - pronunciation, word origin, samples and idioms. I consider it very synoptical and easy to use. I also used to have a programme in my computer. This programme included some English crossword, games etc. that I was using a lot when I taught English some younger pupils.

Other interesting site is Thesaurus. Everybody who writes some longer texts in English, or writes more frequently, tends to repeat himself - at least when you are not very experienced writer. This site is very helpful for everybody who wants to find some new possibilies and broaden vocabulary list.

I was also always a bit interested in etymology of the words. If you also have similar hobby, then you should visit worldwidewords. The author explains a lot of interesting word phrases and you bet that you do not know most of them.