If you are a writer, check out the Writing Aid, an iPhone app by Benjamin Mayo. The interface couldn’t be simpler. Launch the app, type in a word or phrase, and a banner appears at the top of the app, scrolling side to side with a list of synonyms. At the same time, the definition of the word appears in the main body of the app.
Tap a synonym to jump to a new page with more synonyms and a definition of that word. And so on. You can tap on the upper left of the screen to climb back out to previous synonyms.
Simple, elegant, effective.