Google Opinion Rewards : It will give you surveys to answer and you'll get play credits in return to buy premium games/apps/IAP/subscription.
Look Up Pro : Pop up dictionary. Just highlight the text and select Look Up Pro from the context menu. It's so handy.
ADM : One of the best downloader on Android. Its media sniffer is so powerful, it even have m3u / m3u8 playlist converter. The build in browser is so powerful with ads blocking and pop up blocker, it's worth 7sing as second browser too.