Wow, I thought I was the only one! Yeah I listen to Opeth a lot when studying, most kinds of music work but I particularly like metal and death metal because the vocals aren't near as distracting as say, rap, because they sound more like instruments and the melody is emphasized more than the words.
I think I probably listen to BWP and Damnation the most while studying, especially if I'm staying up late, Opeth is more night music for me.