I've seen Mono and This Will Destroy You live in the last 2 months, and they were great. Mono especially just had this engulfing, jaw-dropping wall of sound that was everything I could have ever wanted. I saw Explosions in the Sky last summer, too, and they were great. Some other bands I particularly like are Saxon Shore (though they can be a little predictable), Collapse Under the Empire, and Yndi Halda. All great bands I heard about through last.fm, so I'm very fond of last.fm's recommendation system.
Of course, there's the obligatory Mogwai and Godspeed You! Black Emperor responses. I finally bought "Lift Your Skinny Fists..." and it is an absolute masterpiece of Post Rock.
I remember when I was first getting into Mogwai, every hardcore Mogwai fan I found badmouthed "Mr Beast" to the ends of the Earth, so I discounted it as a crappy album. However, I finally bought it when it was the only Mogwai I could find at Best Buy, and it quickly made it in to quite possibly my Top 10 all-time list, and certainly in my Top 5 for Post Rock. Sure, it's a little different, but it's beautiful. I even bought "Zidane" because I thought "Mr Beast" would make me less of a fan, and since I've bought Mr Beast, I've only listened to Zidane like once, to help me go to sleep. "Hawk is Howling" is still a good album, too, but didn't have the same effect as "Mr Beast" for me, personally. However, "Come on Die Young" and "Young Team" are sort of their personifying albums.
Also, I just went to Mogwai's site. Is anyone preordering this new album? I may do the Premium one for the triple LP...