Merriam-Webster has recently released its dictionary app in the Android Market. Available for free, this application is ad supported.
Features:
- Synonyms & Antonyms
- Voice Search
- Example Sentences
- Audio Pronunciations
- Word of the Day
- Reader View – lets you hide navigation buttons to see text in full screen
- Recent History – lets you keep track of the words you’ve looked up

Does it work offline?