Android is already most popular mobile platform and thousands are joining Android platform every second. Android provides reach set of APIs to build apps for literally everything that can be done on web.
This means there is immense potential for increased content consumption and so it makes lot of sense to build Android apps that help you generate additional revenue on side.
Following are some of very popular Android videos playlists to learn Android Programming for everyone.

The New Boston



Udacity - Developing Andriod Apps