I doubt you will find any major development that focus only on Android as a development platform. Also, what fields are you interested in? A firm that develop games won't be in any direct competition with a firm that develops office software, so comparing them won't be fair.
If you are just talking about income wise.... actually I have no idea about that either since Angry bird is free on Android. Gameloft perhaps? Probably not the biggest money maker in the android playing field, but they are pretty famous.
