Shahi has a great visual dictionary for kids. When searching for a word, this dictionary gives images from Flicker, Google and Yahoo along with parts of speech and a definition.
All pictures shown on my searches were appropriate. Of course if a student types in an inappropriate word, they will get inappropriate pictures. I would use Shahi on my Smart Board so that I could control the search. Shahi is a great way to introduce new vocabulary or look up new words.