Yeah, Signs Reign Rebuilder is a good record. Not one of my absolute favorites, but it's up there. So far as post-metal is concerned, you ever listen to Neurosis? If you like Isis and Pelican I think chances are good that you'll really dig them. Would also really recommend Cult of Luna.
I'm a big fan of the new wave of black-metal (US and otherwise) myself--Ash Borer is certainly a good one. You might like Agalloch if you haven't tried it already--assuming you can get past the singer's voice. It's a real turn-off for some people, and even though I love the band, I find myself still sometimes having to steel myself in preparation for listening to the dude. You should also look into Alcest, Deafheaven, Wolves in the Throne Room, Blut Aus Nord, Negura Bunget, and even some older BM, like Burzum and Ulver. All have a strong post-rock/shoegaze influence, and are great not only as a gateway drug for 'real' black metal, but are just amazing in their own right.
I think ultimately that's the thing I appreciate most about post-rock--it seeps into so many genres. From post-rock you can jump into jazz, classical, chamber music, electronica, post-hardcore, punk rock, folk, shoegaze, sludge metal, post-metal, black metal, drone, minimalism, ambient, whatever, because post-rock is such a 'wide' genre with so many influences--it's really almost the ideal genre to get into if you're interested in widening your musical tastes.