Here's an article about language tools that you can use to help you with your English.
It's mostly about tools from Google. I'll post some other tools I use here and you can add your own suggestions in the comments.
This is a handy set of dictionaries that sits on your computer screen, but this Norwegian company has started charging an annual fee for use which I think is a bit expensive.
I like this dictionary because it gives you a lot of info and even a sound file for pronunciation help.
Another good dictionary: