Vietnamese<>English Dictionar This Vietnamese/English dictionary has 10,000 words! This is the trial version, gives you a peek at the full dictionary for a few uses.
L-Lingo Learn Vietnamese Free This app is really easy to use and teaches Vietnamese through audio, words, photos, and more. Teaches you words and sentences that are very functional for travel, work, and basic Vietnamese conversation.
Byki Vietnamese This is a fun, comprehensive language learning app with photos, written words, and audio pronunciations of the words. It costs $9.99 but is worth it as you really do learn from it. It has lots of learning features like quizzes and you can share your progress to Facebook.
Learn Vietnamese WordPower This is a great, small, free app that teaches you one Vietnamese word per day through text in Vietnamese, Romanized - and audio pronunciation.