Minecraft wiki entry for Block_of_Redstone, associated text: powers any adjacent redstone dust, including above or below, to power level 15
powers any adjacent redstone comparators or redstone repeaters facing away from the block of redstone to power level 15
activates any adjacent mechanism components (doors, redstone lamps, etc.), including above or below, with the exception of pistons, which cannot be activated by any power source directly in front of them