I just discovered Sphero and I love this little ball, so I want to develop apps!
Is there a common coding language that most of Sphero's app developers use so that I can learn it and start building?
From glancing over this page http://developer.gosphero.com. You can use Java for developing on the Android platform and Objective-C for iOS. Looks like there is also a plugin for Unity that uses C#.
That webpage also contains guides for the individual platforms and examples.