Weather Underground combines a slick design with a focus on really useful weather information. We particularly like the ability to report weather conditions in your area and the extremely useful comparative forecasts that deftly show how conditions have changed since yesterday. With an accompanying set of useful widgets, it's the best weather app on Android.
Google Opinion Rewards is appropriately named. Google sends you surveys that ask you about places you've visited recently and you get Google Play Store credit for your participation. Polls don't come in very often, but you can increase your chances of receiving more, by enabling your location and answering surveys quickly and honestly when they do arrive. It's not going to earn you a ton of store credit, but it's enough to purchase an app or an album every so often. To add some perspective, one of our editors has earned about $64 since installing the app in late 2013. Droid App