Hold control and place a block, it will place as many as possible in that direction till it hits something or you run out of blocks to place. Very useful for bridge building. Even in creative, it will only place as many block as as you have in the stack! It can do both vertical and horizontal placement.
Detail and download: Fast Building Mod 1.8/1.7.10
Homepage: Minecraft Mods | Minecraft mods 1.7.2 | Minecraft mods 1.7.10