The important thing to recall about radiohead is that their sound changes significantly from album to album. The Bends is more like alternative rock, OK Computer is alternative rock with a lot of electronica overtones, and it's darker than The Bends. Kid A isn't really rock at all, Amnesiac is even more depressing (imo). Hail to the Thief starts the trend going back the other way, getting a bit more movement and rhythm, but still really really dark. In Rainbows is brighter in mood, but a lot of people seemed unsatisfied by it.

Songs I like, according to my iPod:
The Bends: The Bends, Black Star, My Iron Lung, Street Spirit (Fade out)
OK Computer: Electioneering, Exit Music (for a film), Lucky, No Surprises, Paranoid Android
Kid A: Everything in its Right Place
Amnesiac: Pyramid Song
Hail to the Thief: Go To Sleep (Little Man Being Erased), Sail to the Moon (Brush the Cobwebs out of the Sky), Sit Down, Stand Up (Snakes & Ladders), Where I End and You begin (The Sky is Falling In)
In Rainbows: Jigsaw Falling into Place, Reckoner
Misc Live: True Love Waits, 15 Step

15 step is on In Rainbows, but I like the live version a lot