Minecraft wiki entry for Redstone_Comparator, associated text: Furnace
Blast Furnace
Smoker
Brewing Stand
Hopper
Minecart with Hopper on top of a detector rail
Dispenser
Dropper
Chest
Trapped Chest
Minecart with Chest on top of a detector rail
Barrel
Large chest
Large trapped chest
Shulker Box (any color)