Big question. Big. Full-length studio albums only, no EPs/extra discs/live releases. I haven't listened to all of the albums in anywhere enough depth to make a strong decision but off the top of my head it looks like:

1) OK Computer
2) The Bends
3) In Rainbows
4) Amnesiac
5) Kid A (despite Idioteque being in my top five songs of all time)
6) Hail To The Thief
7) Pablo Honey