Minecraft wiki entry for Redstone_mechanics, associated text: Redstone Repeater (as if "attached" to the block it is facing)
Redstone Comparator (as if "attached" to the block it is facing)
Buttons
Detector Rail (flat only; also produces comparator updates)
Lever
Pressure Plates
Trapped Chest (as if "attached" to the block beneath; also produces comparator updates)
Tripwire Hook
Weighted Pressure Plates
Observer