Apple's GarageBand has no equal in the iTunes App Store with its tons of cool features for making and recording your own music. The Smart Instruments that make beginners sound like pros mean everyone can create great-sounding songs--on their iPhones! Unfortunately, Android users are out of luck because there still isn't an Android-based equivalent that's quite this good.
One of the early great apps for taking retro-looking photos is still going strong in the App Store for good reason. Hipstamatic's tons of lenses, filters, and flashes mean you can experiment with making really cool images.
Since there isn't a Hipstamatic for Android, Retro Camera is a popular Android application that lets you take six different styles of nostalgia-inducing photos.
This Scrabble clone with a slightly different playing board and rules was an instant hit among word game fans on the iPhone. Easy connection with friends and push notifications make Words With Friends an easy way for pals to stay in contact and play a fun game.
Whether you're comparing restaurants or veterinarians, Yelp gives you access to tons of reviews from other actual users of products and services. It was already a great idea for the Web, but on your smartphone it's a must-have for finding nearby treats.
One of the only games to consistently challenge Angry Birds at the top of the most-popular lists, Cut the Rope has become its own puzzle-gaming success story. It probably doesn't hurt that the game's mascot, Om Nom, is such a cute little alien.