Lingro which the creators call a dictionary.
At first glance it does not look like a dictionary because it is more than a dictionary! You can paste the URL of a website and then click on any word - Lingo will give you the translation. It translates words from / into 11 languages! And what's more - it will save the words that were translated for you in your history (to save the list you have to register). You can go back later to review the words and learn them. What an easy way to get the meaning of an unknown word instantly!
Lingro does it with a simple text file too! Just upload the file and start translating!
If you think you'd like to use Lingro services constantly, you can download the browser plugin (it offers Firefox extension) and you will be able to translate ANY word on ANY page you are viewing.
Great tool for learners of languages!