Tap-Translate is a new app (or really, a bookmarklet posing as an app) that translates words in foreign languages right from your phone's browser. No exiting the app, no switching, no fuss. That means whenever you stumble upon something you don't understand you just click on the bookmark, tap on the questionable word and let it translate.
The app can display the word, say the word out loud and even translate the entire page. Definitely worth it if you find yourself stumbling into foreign sites often. $2.49 (iPhone) or $2.05 (Android). [iTunes, Android Market]