I haven't been this impressed by an online tool for a very long time - Lingro allows you to view any webpage or word/pdf/text document in your browser and instantly get a translation or definition of any word on the screen.
From there you can also create your own wordlists and then play a flashcard game to test your knowledge of the translations/definitions. You can also click on a speaker icon in your translation/definition to hear the word being pronounced.
It's slick looking site that just works really well - it takes a few moments to load up but after that you're off and running. You can also add a button to your browser called "lingro this page!" that will allow you to view whichever page you are looking at in the lingro viewer.
Truly awesome. (Click on images for full sized view)
