Yeah, agree with the Dirty Three. Very nice, albeit also very melancholy and driven by an extremely talented violinist, so keep that in mind. I'd go with Ocean Songs myself. Some other favorites that I don't think have been mentioned yet ...
Cul de Sac - Crashes to Light, Minutes to its Fall (I've talked about this one quite a bit here)
The Appleseed Cast - Low Level Owl: Volume 1 (doesn't follow the same soft-loud-soft "formula" as Mogwai and GYBE, but similar goals and it works very well)
Tortoise - Millions Now Living Will Never Die (Djed - a classic)
Kinski - Be Gentle with the Warm Turtle (I like the last one a lot too, Airs Above Your Station, kind of a Sonic Youth meets Brain Eno sound)
Hash Jar Tempo - Under Glass

-))
Rachel's - The Sea and the Bells (neo-classical at heart, but one of the most brilliant, refreshing albums to come out of the mid 90s post-rock scene. 17 musicians and 23 instruments, including contrabass, viola and bass clarinet, have here been drafted to perform and record this gorgeous, sprawling epic - required listening)
Spiritualized - Ladies And Gentlemen We Are Floating In Space (essential modern space rock)
Voyager One - Monster Zero (MBV meet Echo & The Bunnymen)