Providing an overview of the life of an artist you admire can be a strong research topic. There will be more than enough information, and in some cases, you may need to narrow it down to a single aspect of the artist's life or an era of her work. You could provide an overview of Mozart's life and some of the controversy that surrounded him because of his eccentricities. Additionally, his work was so prolific that you could focus on one era of his life and then detail compositions from this period.
Researching a genre will involve researching numerous composers, their compositions and their relation to historical events of the time. This can also include historical performance practices or modern developments in the genre. A genre such as jazz could be very involved, and this is a younger genre in comparison to others. You could discuss important composers throughout the history of the music, beginning with ragtime and moving up to modern artists who fuse jazz with world music. Equally as involved could be a discussion of innovators from each era and performance practices, such as using standards from the Great American Songbook as vehicles for improvisation.
Music written for the same performing ensemble will often have certain stylistic elements in common. Researching this will involve comparing numerous composers' works for similar ensembles. Examples of this include string quartets, symphony orchestras, big bands, chamber orchestras and small jazz groups. This topic will also allow for analysis of the pieces you are comparing as well as highlighting a lineage of composers and their students.
Professional issues in the music field can offer a unique perspective. Many people do not view music from this angle, so this can allow to paper to have a fresh view for the reader. You can discuss employment by musical organizations, music education, music therapy, pedagogical philosophies or performance anxiety among countless other issues.