Jisho.org is probably my most favourite online dictionary. Why? -It’s simple to use and in my opinion is very useful.
What makes it easy? Many functions available: you can type, draw it, choose from radicals or say the word.
When you look up a word, translation is given. Also, you can see kanji and other words that might have the same kanji.
What I like about jisho is that you can paste full sentence and it will break it down. It will separate words and if you click on the particle it will give info about it. It will also recognize verb in different forms and say what is this form usually used for.
What else can jisho do?
I think jisho.org does a good job, I am not sure about other online Japanese dictionaries since I use this one. If you know any other good online dictionary for Japanese tell me in comments ^.^