Again, I can't take credit for this idea, but I <3 it.
If you haven't heard of Pandora Radio, it is an online radio that you can stream to your computer for 40 hrs a month for FREE!! and apparently after that it is really cheap to continue to listen says my hubbie.
I have an account hooked up to my school email and we listen to it all the time. I have a Disney channel for morning time. I personally like to sing along as my 4th graders walk in and give me strange looks. Secretly I know that this is one of the things that makes my students love me. Although that is not any sort of goal of mine, it really helps that the students love you.
For working time, I usually have a jazz or classical station playing in the background. Most of the students want to listen to the music and they keep each other in check...I hear a lot of "shhhh, I can't hear the music!" Sometimes peer pressure is a GREAT thing.