A recent move by Collins Dictionaries, I believe. Dictionary in English, French, Spanish & German, with soundfiles, thesaurus and rudimentary translation to several other languages. It also links to a site that organizes professional non-machine translations:
My initial finding is that you should view it in LANDSCAPE on a Kindle 3, as the default view cuts out the initial search box. Once you have got your definitions, you can view them better in ARTICLE mode. Despite the initial problem in searching from the start page, the rest of it seems pretty easy to use on a Kindle. The database is a bit limited at the moment, but Collins intend to make it much larger by-&-by.