Opeth is still a favourite band of mine, even though I don't really listen to metal nowadays. Sadly enough I wasn't old enough to see them when they came to NZ (I was a few days short of 18). Martin Mendez is one of my bassist idols.
I second the Agalloch recommendation. That was my study music back in high school.
I started with Pale Folklore but I think that the Mantle would perhaps be the best to start out with.