iOS: NoCrop for iPhone and iPad lets you avoid having to crop your photos before you upload it to social networks like Instagram. The app achieves this by adding the necessary whitespace around your photo to make it fit.
It's a little frustrating to upload your photos to Instragram (and services like it) that want to crop your photos to squares when your phone is capable of taking beautiful wide sweeping photos or long portrait shots. NoCrop steps in by giving you the ability to add white borders around the top and bottom of your widescreen shots or the left and right sides of your portrait photos. When you import a photo, the aspect ratio is automatically set to Instagram's requirements, and you can tweak the size of the final image in the app.
Before you hit upload, you can choose to share the same photo on Twitter and Facebook in addition to Instagram or to just save the final product to post later. Keep in mind that by adding whitespace on any side you decrease the size of the viewable part of the photo. The app is completely free and available now in the iTunes App Store.