I can't get enough of this lately. St. Nektarios of Aegina wrote this wonderful hymn and it is sung during Orthodox Vespers. I listen to it in Greek - by Divna Ljubojevic (angelic), another version (don't know who is singing this one) and in Arabic.
But my favorite is sung by the Valaam monks:
You can sing with them, here is the Old Slavonic version transliterated in Russian and English