I'm the type of person who can't study without any distraction. If it's too quiet, I end up sleeping, so I mostly studied in front of my PC or with some music on. haha
I listen randomly, but mostly calm ones... though I also sometimes listen to fast beat ones to keep myself awake. Here are some of my recommendations:
It's Brand New Breeze by kanon. It's from the anime La Corda d'Oro. :)
Aside from this, I also enjoyed listening to UtaPri songs like Canon by Mamo-chan
and Prince of Tennis character songs like Wonderful Days.
I hope you enjoy them... :)