We do! Our's is "What I Am" by Will.i.am (Sesame Street). It's a great song to play in the morning as students are coming in/end of day when students are waiting to leave. My kids like to act it out as they're singing. For example, when they hear the word stronger, they flex their muscles. Sometimes I Youtube the lyrics version and we practice our fluency by reading the lyrics.
I found this treasure on Pinterest, of course, and had to share it with my students. We voted on it to be our class theme song. It's catchy, positive, and even though it's Sesame Street, my 4th graders love it. I guess Will.i.am helps give it "cool" status. On a scarier note, we had an unexpected lockdown earlier in the year and afterwards my students suggested we cover the door window like some of the other teachers so that if there ever were an intruder he/she couldn't see us hiding. To ease their comfort, I took black construction paper and wrote the lyrics to our theme song with neon chalk paint. I hung our lyrics in the window of the door. Now whoever's first in line is reading & practicing their fluency while waiting on others to line up/at random times throughout the day & the window's completely covered. Win-win ;)