Here's a link that's going round to a nice online tool. Just go to the web page, enter the URL of a web page you would like to read. The site will process the page and then allow you to click on any word on the page to get translations. It also allows you to add translations for words not already listed.
Available for English, Spanish, French, German, Italian and Polish
Also spotted this Visual dictionary which is not a new idea but a really nicely done one. You enter a word and then the dictionary shows you all sortes of connected words and their relationships. Nicely colour coded. With mouse over translations. Probably a tool for the more advanced student, but really well done.
Nik Peachey | Learning Technology Consultant, Trainer, Content Designer