ObjectGraph has a basic dictionary web app with ajax that’s worth mentioning.
Type in a term and the results appear as you type each letter. It works much like Google Suggest. There are a number of dictionary options, and a thesaurus. From Download Squad.
Personally, I find this firefox extension dictionary much more useful – but ObjectGraph’s ajax implementation gets them extra points.
ObjectGraphs’s blog is here and a description of how it works is here.