Well, fourth grade
is too young for what I do. I do hip-hop lyrics (appropriate ones) as a big part of my poetry unit. Could you do songs like Simon and Garfunkel stuff? There are a lot of literary devices in those songs that are pretty easy to point out and understand. Maybe you could do hip-hop if you did Will Smith. I hear he's real clean, no drug references. I mean, I don't do foul language or gang or drug references with my kids, either, but I still wouldn't use most of it with fourth graders. Will Smith might be okay, though.
If you have a lot of Mexican immigrants, you could use songs in Spanish--with a translation for the Anglos. That would be nice and it would be inclusive, also show that literary devices happen in other languages, as well.
Truthfully, I don't know what fourth graders listen to. I'd probably be horrified. :-) Have a listen to the music they like and see if you can use any of it. I tell you, it's some work initially, but then it's done, for every year thereafter, and kids really, really love and respond to music.