VocabBuilder is Tiger-only, but it makes good use of Tiger's built-in dictionary. This tool keeps a list of words that it displays under the Desktop on the left side of the screen. At any time, you can use Expose to show the underlying window and command-control-D to display a definition.
One World Dictionary by Ascendo is a leading multilingual reference tool for Apple desktops.
InstantTranslate makes it really easy to translate a selection of text in the application you are working in from one language to another language.
Mall Creeps
