I love Enya.
It's especially good if you want to calm down or just sort of meditate a little bit.
For me it also works as background noise.....
Once, a long time ago in a galaxy far, far away when I still played WoW before any of the expansions, I put on my Enya playlist over Vent during an evening clear of Zul'Gurub (we were easily farming it, so communication during fights wasn't necessary, everyone knew what to do). Afterwards, everyone said it was the more relaxing raid they've ever done. Win!