Topic of your choice, provided it relates closely to popular song of the last 50 years or so.
This may be fairly analytical in nature, requiring no research, exactly — just close, careful, thoughtful attention to a given song (or perhaps more than one). If that’s your approach, do your best to attend to music and lyrics both in some way. But this paper doesn’t have to be analytical at all!
There are many things to talk about when we talk about popular song (album art, broad stylistic trends, cultural matters, whatever). You are free to do anything you want. But if what you’re doing is not really analytical in nature, there should be a component of research involved: You should locate and cite sources (three secondary sources at a bare minimum).
Wikipedia doesn’t count, and neither do basic sources for lyrics. And while I don’t forbid you using, say, online reviews as secondary sources, I strongly urge you to press into scholarly secondary literature, too. Do your best to demonstrate that you’ve gone out and delved deeply into your topic. (Here are some ideas about locating appropriate resources.)
If you do make use of secondary sources, citations should take the Notes and Bibliography form described in the Chicago Manual of Style Links to an external site., with footnotes at the bottom of each page and a bibliography of all works cited at the end of your paper.