Baba Satya Sai's Bahajans are very popular as they are very simple, easy to sing and understand. Baba used to stress on singing those Bhajans which contain more names of the Lord rather than any other type, since Nama Japa is advised during Kaliyuga.
Baba sung many Bhajans himself. One of the those which I like most is "Govinda Krishna Jai"
Courtesy: You Tube