I recently found this dictionary. ejje.weblio.jp
I find it so useful when I'm not sure how to use a word correctly in context and what particles are used with it.
Now although I use classic.jisho.org and rikaichan for the meanings of words, I use ejje.weblio.jp for checking the usage of the word.
I think it is geared more towards Japanese speakers learning English, but I'm not really sure.
Nevertheless, what I like about it is that it has a large number of examples I can scan through for most words.
Do you scan through example sentences online when you're studying?
Which online dictionaries do you use? Do you use electronic dictionaries (電子辞 re)?
An electronic dictionary can show you letters bigger as you want, maybe it is nice for Japanese letters because there are much more lines in a letter than in European ones.
Most of the electronic dictionaries sold in Japan contain lots of dictionaries. I would recommend that you also look up dictionaries which are actually for Japanese, "広辞苑" or "漢和辞典”, because there is much more information about the source of words or expressions, such as old Chinese history, poems or religion. For Europeans, some ideas or consensus in Japan are totally unknown. It can make you memorize the word sometimes much easier by associating other information.
"広辞苑" is a JP-JP dictionary and it changes the definition of words very quickly and takes orally used words, too. Therefore it is interesting just to read it through.