Maybe it leans more toward "post-metal", but I've been on an Isis since this spring. Also listened to a few Pelican and Russian Circles albums also which I really loved. Any other post-rock/metal bands that I should be on the lookout for?
The top3 kings of Post-Metal to me are:
Neurosis - Isis - Cult of Luna
Neurosis is my favorite out of the three, and I would also say the most versatile. They have blended various influences on their albums, so you get everything from Pink Floyd on Metal to pure light Post-Rock, and Folk-Rock inspired metal. They're amazing, and have one of the best album runs out of any bands I know.
You already mentioned Isis so I take it you are familiar with their albums. Personally I think Panopticon and Oceanic are just masterpieces, even if the other three aren't on the same level, they're still dope.
Cult of Luna is the hidden gem of the three. Best metal band from Sweden IMO, they also have some really amazing albums. Salvation being my favorite, Somewhere Along the Highway being on the same level. Add other amazing albums like The Beyond, Eternal Kingdom and the most recent Vertikal, and you got a strong discography.