Haven't seen it. Though I've heard a lot of their stuff. I think Sigur Ros are one of those names that get thrown about a lot be those who are trying to sound cool. Most of them barely know anything post-rock beyond that, and possibly 'Explosions In The Sky'.
I've been really into post for about 2-3 years now. I loved the different soundscapes that could be created, and the images and thoughts they provoked.
Now on to bands:
Godspeed You! Black Emperor: Amazing lengthy soundscapes. In particular, the albums F♯A♯∞ and Lift Your Skinny Fists Like Antennas to Heaven
Red Sparowes: Probably my favourite post-rock band. Favourite album is Every Red Heart Shines Toward the Red Sun. Followed by; At the Soundless Dawn
A Silver Mt. Zion: No specific album, but overall a consistant band with a great sound.
God Is An Astronaut:: Same as above
Do Make Say Think: I've only got a few of their tracks, but they're some of my favourites. Been meaning to get around to getting more.
Russian Circles: Another really strong band. The tracks really seem to flow seemless on the albums, in particular Enter.
Slint: Crosses over with Math Rock. Still, one of the early post rock influencers. Spiderland is consistently listed as a great post-rock album.
Stereolab: A large number of albums, so no real definable favourite yet. I haven't got nearly enough of their stuff.
65daysofstatic: One of the first Post-Rock bands I heard. They have a interesting sound, though probably not as good as the ones I've listed above.