Personally, I think that it's a tie between either Power, Corruption and Lies or Get Ready; PCL's flower and color-code combination seems to work really, really well with the music, visualizing the cross between the warmth of the guitars and drums and the cold, electronic rhythms, textures and blips. Get Ready, like its album art, is very crisp-sounding and modern.
What do you think? *points towards the computer screen*